None
None
B ©(•kCnCncncnCnCni^iloCniK •^toen)oajo>o<®'»oo>9>w Thennometer, wet. w iisstsMsiiSS Elastic force. 00 CO Cn(0<OCOCOCOCO®.«*>4CO Ct Per-centage of vapour. 1 1 ^ 1 " ■ 1 f 'S' $ OBSKRVATIONS TAKEN IN INDIA. 341 to attract macb vapour, nevertheless the greatest quantity of rain does not fall at Dodabetta. The mean of the hourly observations once a month, and the mean of the two observations daily throughout the year, giving respectively 87 per cent, and 90 per cent, of moisture in the air at Dodabetta, observation and expectation thus go pretty well together, and the records might be satisfactory, were there not doubts about the manipulations with the wet bulb. The hygrometric observations in the Deccan with Danieix’s hygrometer, which were taken by myself thrice daily, are quite in accord with the feelings and with the expectations of the observer, except- ing for the month of March, in which the feelings indicate the air to be quite as dry as in the months of February or April, but which the hygrometer indicates to be 6 per cent, nearer to saturation than in either February or April. At Aden, in the latitude of Madras, on the arid coast of Arabia, where little rain falls, the mean monthly and annual per-centage of moisture appears unexpectedly high ; the lowest percentage (60f ) is in November, and the next lowest 68^ and 65| respectively in August and sSeptember. The maximum per-centage was 77^ in March, and the mean for the year 71. T^hese results have a certain relation to the phenomena at Madras, which is destitute of a S.W. monsoon. The mean maximum tension of vapour was ’902 in May at Aden. The mean monthly and annual results at the several stations have no doubt a cer- tain relation to truth, as it is seen that the per-centages of moisture or fractions of saturation in the atmosphere in the different months of the year have an increasing or diminishing amount as the several months approximate to, or recede from, the monsoon months of the year ; this is sufficiently shown at Madras, where the mon- soon months are the dry months at Bombay and in the Deccan. Nevertheless the amount of moisture in the atmosphere, deduced from the observations of the wet bulb, is so very great compared with the amount determined by the direct method by Danieix’s hygrometer (itself an imperfect instrument) in the Deccan, and at some of the stations is so little in accord with personal recollections and experience, that 1 cannot refrain from suspecting some error of observation, some mismanagement in the manipulations, or a fallacy in the formula by which the dew-point is deduced from the temperature of the wet bulb. The first cause of error that struck me was that arising from the proximity of the dry to the wet bulb, as noticed by Professor Oblbbar in his Report of Meteorological Observations taken at the Bombay Obser- vatory in 1846. He bad a stand erected out of doors, 6 feet high, and with a thatched roof, and every precaution was taken to guard off radiation by layers of cotton and tow upon a board under the roof upon which the meteorologic instruments were placed : there was lateral access for the tur all round. He soon found that the dry bulb, in the neighbourhood of the wet bulb, was almost always depressed below the neighbouring standard thermometer, and that the depression of the dry bulb was greater as the depression of the wet bulb below the standard was greater. Professor Orlbbab explains this in the following words : — ^“Tbis seems accountable only on the 342 LIEUT.-COLONEL SYKES’S DISCUSSION OF METEOROLOGICAL supposition that heat is extracted from the air to form the shell of moisture round the wet bulb at a distance as far off as the dry bulb.” These discrepancies amounted on the 3rd and 14tb of November, at the 19tb hour, Gdt. mean time:— Standard. 82*4 Dry. 76*6 Wet bulb. 71-8 Diff. ... 5-9 Standard. 82’4 Dry. 75*4 Wet bulb. 69’3 Diff. ... Supposing therefore that the same error was not discovered at the other places of observation as was discovered in Bombay, there is necessarily some ground for the expression of my doubts, whether the air really did hold at the different stations the quantity of moisture represented by the figures I have elaborated. But Professor Orlebar observed another source of error, contingent upon the locality of the wet bulb apparatus, whether placed mthin doors or out of doors. To determine the amount of error he placed a wet bulb wtV/ttn the observatory, observing simultaneously with the wet bulb out of doors upon the meteorologic stand. This was done hourly for March, April, and to the lOtb of May. The reading was almost always plus with the wet bulb inside ; on the 22nd of Marah, at 19tb boor, to the extent of 3®*2, while at 18th hour it had been only 0*2 plus ; but there were great irregularities in the read- ings, being plus or minus dependent apparently upon drafts of air within the obser- vatory, which would depress the wet bulb or raise it. Also the “ atmosphere within the room would tend to keep up a reading at any time to whatever it had been at a time preceding," and the latter. Professor Orlebar says, was the principal oatfse of the plus readings in-doors. Supposing this error of 8® to be applied as a correcticm to the reading of the annual means of the wet bulb at Bombay for 1843, the per- centage of moisture in the atmosphere would only be 65 instead of 78. distin- guished experimental philosopher Bronault has pointed out the same sources of error . He placed the dry and wet bulb in the open air in the court of the College of OBSERVATIONS TAKEN IN INDIA. 343 France, in a closed room in the Coll^, and in the theatre of the CoHege, opening the windows. In the open air, with a temperature ranging from 7°'16 to 17^*88 Cen- tigrade, and a depression ranging from 1°*86 to 9°*60, the results, by observation and by M. Rbonauia'’8 tentative formula*, were sufficiently satisfactory ; but in the closed chamber he says, “Les fractions de saturation calcul^es avec la formule'f', sont ici beaucoup plus fortes que celles que Ton deduit des pes^es directes de I’eau ren- ferm^e dans Fair ; en d’autres termes la temperature i marquee par le tbermometre mouilie n’est pas assez abaissee par la vaporisation de I’eau que se fait ^ sa surface pour donner dans la formule la veritable force eiastique x de la vapeur. Cette cir- constance tient evidemment k ce que Fair se trouve beaucoup moins agite qu’^ I’ex- terieur.” — Page 219. At page 220 M. Regnault adds, “ Ces experiences demoritrent de la mani^re la plus evidente que la formule ne peut pas rester la meme pour les divers etats d’agitation de Fair.” Here then is a second source of error ; and it is somewhat curious that Professor Orlebar, in guarding against another grave source of error, which will be adverted to, himself contributes to an error of observation. He had observed the effect of wind blowing upon the wet bulb in unduly depressing the temperature, and to guard against this he says, “ As it was equally essential that the bulb of this thermometer should not be exposed to the wind, and that it should be in the same body of air as the air-thermometer when the latter was exposed to the wind, a small mirror, about an inch square, was put on a little stand, and this being placed upon the tin board could be moved about by the observer into such a position that it might always cut off the wind from the bulb of the wet thermometer only” (page Ixiii.). Now the wet bulb being thus screened, would be buried in its own vapour and the reading would neces- sarily be too high. When the air is perfectly calm the same would be the result without the screen, for there would be a shell or coat of saturated air round the bulb. I had occasion to notice this local character of aqueous vapour in my Meteorology of the Deccan, where I constantly witnessed it, as regulated in its distribution by nature. Speaking of dew, I said in the year 1828, “At Marheh in the Pergunnah of Mobol, garden produce (which is usually irrigated during the day-time) was covered ^tth a copious dew every morning ; the lands bordering the gardens for forty or hfty yards around were slightly sprinkled with it, but there was not a veetige qf it ija ,t;be fields constituting the rising ground north and south of the tract of garden land.” Hence I inferred that “ aqueous vapour had been taken up by the action of the sun during the day, suspended over the spot, and deposited by the lower temperature at mgbt as dew upon the land in proportion to the eopply obtained by day.” My tents were within 200 yards of the fields where I observed these phenomena, but from the 1 1th to the 30th of January 1828, there was not any deposition of dew about them, ex- ceptii^ on the 13th of January. In consequence of these observations I was induced t ^ 0-4290-/') •-f eid-/'" H. * Aastles de Chimie, tom. xv. p. 218. S44 LIKUT.-COLONEL SfKBS'S DISCUSSION OF METEOROLOGICAL to remark particularly the localities of dew at Poona and in its neighbourhood. In September and October I found that when there was not a trace of dew in the can- tonment, there would be a deposition on the fields of standing grmn half a mile distant, and when there was not any dew either in the cantonment or in the fields, it would yet be found on the banks of running rivulets and on the banks of the Mota Mola River ; but with respect to the rivulets, ‘‘Jifteen or twenty feet from the water were the limits of the deposition” 1 gave numerous other instances of the local deposi- tion of dew proximate to irrigated lands, or in the neighbourhood of water, indicating the suspension of vapours over the localities, in complete analogy with what occurs to the wet bulb thermometer when the air is calm. That agitation of the air is necessary to disperse the vapour surrounding a wet bulb, has been noticed by British chemists. Brand says (page 111, last edition), “ It is now established that the pres- sure of air is really an obstacle to evaporation, and that a current is useful, not by suppljring new quantities of air, but hy removing the vapour according as it is formed and leaving fresh spaces into which the vapours may expand.” He elsewhere says (page 82), ** Evaporation is proportional to the surface exposed ; it is also accelerated by agitating the superincumbent air, as in the case of a brisk wind, or by artificial means. When the air is tranquil the vapour rests upon the sutface of the water, and it is the pressure of its own vapour on the surface of a liquid, and not that of the gaseous atmosphere which stops the process.” M. Rbonadi.t has demonstrated the truth of this in an elaborate manner. Accounting for the ditferent results of observations in a closed and open chamber, be says the wet bulb was not sufficiently depressed in the closed chamber. “Cette circonstance tient 4videmment k ce que Fair se trouve beaucoup moins agit^ qu’^ I’ext^rienr*.” After experimenting in a room udth two windows open, he adds, as before stated, “ Ces experiences demontrent de la mani^re la plus evidente que la formule ne pent pas rester la m^me pour divers etats d’agitation de Fair.” (P. J’m cberche k determiner par des experiences directes, I’influence de cette vitesse et k reconnaitre si, ^ partir d’une certaine valeur de la vitesse, les differences de tempera- ture des thermometres sec et mouilie deviendraient independentes de la ^tesse absolue du courant d'air, consequence k laquelle on se trouve naturellement conduit par le raisonnement que M. August applique au calcul de la formule du psycbro- metre.” M. Regnault then describes his apparatus and mode of making bis experi- ments. He gives two series of experiments ; in the second experiment the air being made to blow upon the wet bulb with a greater velocity than in the first. It will be sufficient to give the first and sixth figures of each series. Annales de Chiinie« tom. xv, p. 219. OBSERVATIONS TAKEN IN INDIA. 345 1st series. 0 1st experiment 14*66 7-2B 7*38 Centigrade thermometer. 2nd experiment 14*96 4*33 1 0*63 Centigrade thermometer. 2nd series. 1st experiment 21*48 10*78 1 0*70 Centigrade thermometer. 2nd experiment 21*70 8*56 13*14 Centigrade thermometer. In Fahrenheit’s scale. 58-37 45*10 13*27 58-93 39*79 19*14 70-66 51*40 19*26 71-06 47*41 23*65 In the first series, in the second experiment, the wind blows faster than in the first, ‘ and the wet bulb is reduced nearly 3°, and the difference between the wet and dry bulbs is increased from 7^*38 to 10^*63, while the temperature of the dry bulb is only raised 0®*30. In the second series the temperature of the wet bulb is reduced from JO°*78 to and the difference between the wet and dry is increased from 10°*70 to 13®- 14, while the temperature of the dry bulb is only raised 0®*22. Upon these experiments M. Reonault says, ‘‘ On voit que, pour une ineme temperature / les temperatures dependent beaiicoup de la vitesse du courant d’air” (p. 209) ; and he further says (p. 210) that these depressions are less than he has found on other occa*- sions with an increased velocity of the air ; and on using dry air he found the depres* sion /'=13®-52 instead of 5®-9I, and another depression of 15®-60 instead of 8°-60. M. Reonault gives other experiments, and finishes by saying, “ II rdsuite de tout ce qui vient d’etre dit, que Fagitation de Fair doit exercir une influence trfes- sensible sur les indications du psyebromfetre” (p. 21 1). The truth of M. Rbonault’s experiments are borne out by the experience of families in the Deccan (and no doubt elsewhere) in India in the fair season, who cool their wine and beer by the following simple process down to a temperature the cold of which makes the teeth ache in drinking. At any time of the day a thick layer of straw is put down on the ground in the shade of a building, but not in the lee of the wind. t My aeueations deceived me. While this paper is going through the press, I have received from a friend, commandmg the Artillery at Ahmednugger, the following results of experiments he made at my request, with MDCCCL. 2 Y 346 UEUT.-COLONEL 8VK£S*S DISCUSSION OF MSTfiOROLOOICAL the bottle of wine or beer corresponding to the bulb of the thermometer ; the straw lying thinly over it represents the muslin, and the operations of the watering-p-pot com- plete the wet bulb apparatus, evaporation does the rest ; but as the velocity and dryness of the wind regulate this, it is plain that such an instrument can only give imcertain and fallacious results when used to determine, with any pretension to accuracy, the fractional saturation of the atmosphere. I come now to a source of error in my reductions of the wet bulb observations which I have collected in this paper from various parts in India, a source of error that may operate with a greater or less power as the depression of the wet bulb is greater or less. I allude to the formula used for the reductions of the readings of the wet bulb. M. Regnault says that M, Gay-Lussac was the first to propose the determination of the dew-point by the observations of a dry and wet bulb apparatus*, but that to effect the object satisfac- torily it would require extensive observations upon which to found tables. Subse- quently to the period of M. Gay-Lussac*s proposition, August, Professor at Berlin, occupied himself with the subject and published some papers, in which he sought to determine, upon theoretical considerations, the formula by which the elastic force of aqueous vapour, really existing in the air, could be found by the difference of temperature of a dry and wet bulb thermometer. The dry and wet bulb apparatus he called a Psychromfetre. His chief memoir is published in the Annalen der Physik und Cbemie, V. Band. Leipzig, 1825. August’s formula was x= y A, where t denotes the tempe- rature of the dry bulb (in Centigrade degrees), the temperature of the wet bulb, 7 the specific heat of dry air, 2 the density of aqueous vapour, k the latent beat of aqueous vapour between the temperatures t and » the specific heat of vapour, A the height of the barometer, f the elastic force of vapour in saturated air at the temperature and x the elastic force of the vapour actually existing in the atmo- sphere ; X,/' and A being expressed in inches, or in terms of any common unit. the wet straw process, on the 2l8t of May 1850, and preceding days. Temperattne of air in shade, free from radiation, 98* Fahr. Temperature of water in bottles under wet straw exposed to wind 65*, difference *38*. The dew-point by Apjohn's formula would be about 41®’7, and by Qlaishxb*b factors about 48**5. My friend says, ** When the wind does not blow, the temperature of the water in the bottles, under the straw, cannot be got lower than 71* Fahr. When the wihd blows, the bottles cool to 65* Fahe.” ♦ Annales de Chimie et de Physique, 2nd series, t. xxi. p. 91. OBSERVATIONS TAKEN IN INDIA. 347 With assumed values for 7, i and K, as the real values are not accurately known, and neglecting small quantities, and supposing assy, August's formula became O428(f~0 640-/ for the determination of the elastic force and consequently the dew-point, and after certain comparisons of the dew-point from his formula with the direct dew-point from Daniell's hygrometer, he found what he considered a sufficient agreement be- tween them. In a comparative table* of the results by his formula and the results by Daniell’s hygrometer, they appear to go pretty well together, while the variations of temperature and of the depression of the wet bulb are small ; but the moment the temperature exceeds 20° Centigrade (68° Fahr.), and the depression exceeds 5° (9° Fahr.), the discrepancy is very considerable ; for instance, at bar. 755*3 milltms. (29*736 inches), dry 28°*5 (83°*3 Fahr.), wet 21°*1 (69°*98 Fahr.), depression 7^*4 (13°*32 Fahr.), the tension of vapour by the formula is 14*181 millims. (‘558 in. =dew-point 62°), and by Dakiell's hygrometer 12*087 millims. (*475 in.=dew-point 57°' 15), the difference 2*094 millims (*083 in.). Even with a depression of only 0*6 (1°*08 Fahr.) the tension of vapour by the formula and by Danirll is respectively 8*612 millims. (*339 in.), and 8*534 millims. (*335 in.), difference 0*078. These discrepancies induced M. Regnault to modify, in 1845, nearly twenty years afterwards, August’s formula, and he in common with August assumed y=0*2669, J=0*622 and *=y, but X=610— Substituting these numbers and neglecting small quantities, the formula became and it is this formula that M. Regnault tests by his various experiments ; and at the close of his able and ela- borate paper he says, Je ne pense pas que Ton puisse admettre comme base du calcul du psychrom^tre Thypoth^se fondamentale adoptee par August: k savoir, que tout fair qui fournit de la ehaleur au thermometre mouill^ descend josqu’il la temperature indiqu^e par celui-ci, et se sature compl^tement d’humidit4. II me parait probable que la portion de Fair que se refroidit ne descend pas jusqu'^ et qu’elle ne se sature pas d'humidit^. Le rapport de la quantity de ehaleur que Fair enl^ve k la boule par vaporisation de Feau, k la quantity de ehaleur qu’il perd en se refroidissant, est probablement d’autant plus grand que cet air est plus sec, pareeque dans cet £tat, il est beaucoup plus avide d’humiditd que quand il approche de son £tat de saturation. “ Enfin, la temperature de la boule inouill^e est influenc4e encore auti^ement que par Fair imm6diatement ambient, elle est soumise au rayonneinent de Fenceinte dont Finfluence sera variable suivant V&tat d’agitation de Fair. Il me parait impossible de faire entrer toutes ces circonstances dans le calcul thdo- retique de rinstrument ; est je crois qu’il est plus sage de ne faire servir les consi- derations theoretiques qu’4 la recherche de la forme de la fonction, et k determiner ensuite les consiantes par des experiences faites dans les conditions d£termin6es. Cette * Axmalen der B. v. p. 87. 2 Y 2 348 LIEUT.-COLONEL $YKES*S DISCUSSION OP METEOROLOGICAL inani&re d’op6rer rae parait d'autant plus n^cessaire, qu'il reste beaucoup ^incertitude sur plusieurs des elements numdriques que entrent dans le calcul, no tarn meat sur la chaleur spdcifique de Vair^ sur celle de la vapeur, et sur la chaleur absorb^e par Veau larsqu^eUe se vaporise dans tairJ' — (P. 212.) These are the opinions of M. Regnault expressed twenty years after August bad invented bis formula^ and after bis own elaborate experiments ; and 1 have preferred giving them in his own language to free myself from any possible misconstruction in translation. M. Regnault thought that August's formula modified by him, would meet some of the difficulties expressed by him in the above quoted opinions, and he gives tables of results, which, with a limited range of the thermometer and small de- pressions, are sufficiently satisfactory ; but he candidly admits i’accord a beau^ coup moins parfait dans les bas temperatures et dans fair tr^s bumide in these cases M. Regnault says the fractions of saturation calculated are always above the frac- tions of saturation obtained by direct means, often to a veiy notable extent. M. Reg- nault got one of his pupils to tiy the psychrometer, under considerably diminished pressure, on the mountains in Switzerland, but the results were so little satisfactory that he does not give a detail of them. He induced also his friend M. Izarn, to compare the readings of the wet bulb in the Pyrenees, at a pressure of 700 millims. (27*559 in.), with the readings of an hygrometer invented by himself, which he calls “ bygromfetre condenseur,” and which he considers to be free from the objections to which Daniell’s hygrometer is subject ; and in a table given, the fractions of saturation are almost always much higher by the wet bulb than by the condenser, the depression in no case exceeding In a depression of l®-97, the differences of the fraction of saturation are respectively 0*7542 and 0*7937. Finally, M. Regnault says that his modified formula may give the elastic force of x a little too high, and that the coef- ficient 0*480 might be used instead when the fraction of saturation exceeds 0*40 Cen- tigrade, but that the coefficient 0*429 gives results nearer to the truth where the fraction of saturation is below 0*40. ^ J e ^ so * OBSERVATIONS TAKEN IN INDIA. 349 and fioally, with the coefficient and with this formula*)* Colonel Boilbau of the Bengal Engineers, in charge of the Magnetic Observatory at Simla, to aid meteorologists, has calculated a series of tables of the tension of vapour from minus 10 °Fahb. to 170 °Fahb. for 30® of depression of the wet bulb by tenths, and for variations of pressure from 19 inches to 31 inches. It was these tables I used in the reduction of the preceding wet bulb observations ; and it was in the progress of their use, during several months’ labour, that at certain temperatures doubts were raised in my mind respecting the accuracy of the formula, from supposing the fraction of saturation unreasonably high when the depression of the wet bulb was inconsiderable, and unreasonably low when the depression of the wet bulb wiis considerable. The tension of vapour at considerable depressions startled rue, until at last I found in testing the tables that with a depression of the wet bulb of 19° at a temperature of 52° Fahb., and at a pressure of 29 or 30 inches, the results became impossible ; that is to say, the tension of vapour of the dew-point arrived at by the formula had a greater numerical value than the tension of vapour at the tempe- rature of the wet bulb, e. g. Fahr. Bar. o in* Dry bulb 52 30 Wet bulb 33 20640 Difference 19=(a)= 0! 147 (#—0=21794 It is objected that a depression of the wet bulb of 19°, at a temperature of 52°, never can occur in nature but very considerable depressions, both of the wet * ArjoHN’s formula is expressed in English measures ; is the force of aqueous vapour at the dew-point ; /' the tension of vajiour at the temperature of evaporation ; a specific heat of air ; e the latent heat of aqueous vapour; d the depression or difference between the temperature of the air and wet bulb (f—f') ; p the pressure of the air in inches. t Differing little from Augustus formula, and converting it into the measures and scale used by August ; for all practical purposes, the two formula are the same. ^ In a synopsis of nine years’ observations of the wet bulb at Mahabuleshwur, the following maximum de- pressions of the wet bulb occur in the respective months of the year : — In a preceding page it was shown that water in bottles under wet straw, exposed to the wind at Ahmednugger, cooled down to 65° Farr., the temperature of the air being 98°, difference 33°, barometer 28 inches, dew-point by Amohk 41°* 7, by Glaxsbxe 48°*5, SM L1EUT.-C0L0NEL SYKES'S DISCUSSION OF METEOROLOGICAL bulb and of the dew-point, have been observed even in our damp climate at tbe Royal Observatory at Greenwich. For instance, in the records on the 6tb of April 1845, at 6 P.M., the dry bulb was 53°’6, wet bulb 39°‘3, and dew-point by Danibix’s hygrometer 32°. The depression of the wet bulb being 13°‘4, tbe dew-point by Apjohn’s formula would be 14°, by GiiAisBEa’s factors 25°‘8, and byDANiBix’s hygro- meter it is found to be 22°. Which of these dew-points is to be taken to g^ve the rral numerical value of tbe tension of vapour ? At Greenwich, on the 3rd of June 1846, at 4 P.M., the dry bulb was 79°*!, and the dew-point by Danibix’s hygrometer 44°, the depression therefore 35°' 1. But I have recorded in the Meteorology of tbe Deccan, a depression of 61° of Daniell’s hygrometer taking place before tbe deposition of dew ; tbe temperature of tbe air being 90°, the dew-point 29°, at 4 p.h., on the 16tb of February 1828, at Downd, near Pairgaon, on the Beeina River*. Mr. Glaishbb, of the Royal Observatory, a most persevering and able observer, finding from expe- rience that the formulae in use with a constant coefficient did not give satisfactorily tbe dew-points at varying temperatures and varying depressions of tbe wet bulb, adqited a series of factors quite independent of theory, from the results of very ex- tensive comparisons of simultaneous observations of tbe wet bulb with Danieix’s hygrometer. These comparisons extended over several years, and through several thousand observations. OaSERVATlONS TAKEN IN INDIA, S5l timn to Danielles hygrometer, and to which it is no doubt subject, bat which are applicable to all temperatures and all depressions, objections which were urged by M, RBGNAVi;r, and which induced him to invent his '^hygrom^tre condenseur,** an instrument which he pronounces to be free from the errors of Danibll's instrument, but the use of which I have not heard of in England, I have thus reviewed, in extenso^ the possible, indeed the probable sources of error in the very high degree of humidity constantly in the air, as represented by the wet bulb observations made in India, and I have no hesitation in expressing my belief that the results, which I have obtained with the labour of some months, do not re- present the real fractions of saturation of the air at the several places where the wet bulb was observed^; and I am the more confirmed in this opinion, with respect to the Neelgberries, by an oflScer now in London, who resided some time at Ootacamund and kept a meteorological register, who says that if the mean annual moisture in the air had amounted to anything like 90 per cent, it must have been most inconveniently felt in the clothes, hats, bedding and furniture of the residents ; but so far from such being the case, that, with the exception of occasional fogs, the bills were looked upon as rather dry than otherwise. From my doubts respecting the correctness of the de- duced fraction of saturation of the air at places in India, with the formulae I have passed in review, I may possibly except the observations made in the Deccan with Daniell’s hygrometer, which observations have a semblance of truth, although the instrument may be imperfect. Even with a comparatively low mean annual per- centage of 55 of moisture in the air, I would say such fraction of saturation was rather higher than the truth, for during some months of the year in the Deccan the air is so dry that it is difficult to prevent the disposition of the leaves of tables to curl up into hollow cylinders, and the nib of a quill pen is always most provokingly straddling out into the form of a pair of open compasses. By reason of the above-noticed sources of error in the wet bulb itself, and of the inadequacy of the formulae to give a satisfactory value to its readings, supposing the indications to be correct, I have deliberately mt applied any corrections to the read- ings of the, barometer on account of moisture. But even had the instrument been free from erL*or and the formulae exact, I still should have deemed it ineffectual to attempt to measure the moisture in a whole column of the atmosphere from a local observation^ with a view to apply to the barometer, which i-epresents the pressure of an entire column of the atmosphere, a correction for the tension of vapour;}:. Fur- ther, I have doubts of the propriety of applying to the barometer a correction for * Dr. McClelland says, The wet bulb thermometer would add greatly to the value of these results* but there are discrepancies in the register of the instrument m use (at Calcutta) which prwe it to ho imperfect,** Calcutta Journal of Nat. Hbt.* vol. v. p. 554. t ** This instrument [wet bulb] simply indicates the conditions of the air of the place where it is situated : at 100 feet above it the conditions may be very different.'* — GLAisnsa's H^^metrical Tables, p. 16, edition of 1847. * X The capacity of air to hold water in solution, or in a state of vapour, diminishes with the tempe- rature. 362 LIEUT.-COLONEIi SYKfiS*S DISCUSSION OF METEOROLOGICAL moisture suUractiveiy, even.were the tension of vapour satisfactorily determined for the wAole pressure. The barometeryh/& with increasing satumtion of the atmosphere with moisture, indicating the displacement of comparatively dry air by dilated vapour, the density of which is less than that of drier air, and a certain amount of pressure is taken off the bai*ometer and the mercury falls on account of the diminished density and elasticity of humid air ; but as soon as this vapour is condensed into rain the drier air resumes its ordinary density and elasticity, and the mercury mounts again. If the vapour came simply as an addition to the drier air, the density and pressure of the compound should increase, and the barometer should rise ; but this is contrary to fact. I would therefore not apply a subtractive correction for that vapour, which has already acted directly upon the barometer in diminishing pressure by displacing denser air. The object of applying any corrections at all to the barometer, on ac- count of moisture in the atmosphere, is stated to be to obtain from them the pressure of the atmosphere of dry air*;” but as such a state of the air is a physical impossibility as long as there is a drop of water upon the earth to be vaporized, as evaporation goes on at all temperatures, it may be asked, what practical advantage can be obtained from any such determination ? and the more so, may the question be asked, when experimenters are not in accord with respect to the numerical values of the tension of vapour at different temperatures to be applied as corrections-^. On the whole it appears very desirable that to direct means recourse should always be bad, if possible, for the determination of the dew-point, to Daniell’s hygrometer, or to Regnault’s condensing hygrometer ; and short of this, that persevering compa- risons should be made for years, in extended ranges of temperature^ depression and pressure, and at different elevations, to obtain a more trustworthy wet bulb formula, or an unquestionable series of factors. Rain. If it were necessary to suggest caution in generalizations from a limited number of local observations for the determination of the dew-point, caution is equally, if not more necessary in attempting to fix the normal rain-fall even in a narrow area, much less in a district or province. For instance, within the limits of part of the small island of Bombay, seven miles by two miles, the following is the result of observations with nine rain-gauges. The Fort and Esplanade are necessarily proximate; the Observa- tory at Colabah two miles distant, and the most remote gauge at the Government House at Pared, only five miles from the Fort, the other stations being interme- diate between the Fort and Pared. ♦ Glai8Heb*8 Hygrometrioal Tables, p. 12, edition of 1847. t At 32® Fahe. Dalton's tension of vapour, in inches of mercury, is 0*200. at 95®s= 1*50297, at lOS^^s 3*500 in. The Physical Committee of the Royal Society adopted for 32® Fahb. 0*186, and fbr 96®=1-610. and 122® Fahe. 3*542; RBGNAULT.at 32® Fahb., has 0*18124, and at 95®T'AHa. X*64380.and at 122®=3*619. Kabmtx, at 32® Fahe., has 0*17999, and at 95’" Fahe. 1*57789 ; of course different results are come at by the use of. these Cerent values. OBSERVATIONS TAKEN IN INDIA 353 Bombay^ 1849« Bain-fall. ■ Colsbah Observatory. Fort. Esplanade. BycuUa. Chinchpoogly. Aiiy Cottage,  0*35 0*00 0*00 ^■TTIV ^BTnB 0*00 0*04 0-35 0*00 0*30 0*00 0*03 0*05 0'06 0*05 4 0*00 0*70 0-66 1*23 0*65 0*12 ^eITIB 0*00 1 l-SO 1 0*55 0*55 0*00 0*02 0-00 / 0*30 0*46 0*S6 0*25 0*06 Bi iiB 000 0*00 ^ESiiB 8 0*00 t iV 0*00 ^eTiIb 0*00 0*00 0*10 9 0-00 1 0*00 0*00 ^ESi jB 0*00 000 1 0*00 0*00 0*15 0*10 0*^0 11 0-16 0*32 0*00 0*09 0*70 0*30 12 3‘14 1*78 1*35 1 1*06 0*00 1*26 0*82 1*92 0*95 13 0*34 4*00 1 0*00 l-SO 2*16 1*30 14 0*00 1*86 1*70 0*00 0*00 0*00 15 0*00 1*57 1*43 2*25 0*00 1*25 2*18 1*30 16 4*20 4*65 2*10 3-76 4*75 5*00 3*50 6-79 3*70 17 4*61 2*34 2-60 2*22 2*54 2*25 3*30 7-68 3*35 18 0*65 1*01 1*09 1*10 0*06 1*35 3*56 1*50 19 0-16 2*25 1*81 1*34 0*75 2*58 1*65 3*38 1*50 1-77 5*22 2*20 4*55 4*67 4*70 0*90 1-60 0*70 21 3.34 0*43 0*55 0*74 I 3*95 11-10 4*10 22 4*46 4-28 4*38 3*93 5*11 4*70 3*50 7*66 3*40 23 0*10 0*13 0*24 0*30 3*80 6*88 3*70 24 3-62 4*53 5*20 5*22 6*00 6*43 0*43 0*90 0-45 25 3*93 10*51 6-73 7*60 : n-75§ 5*40 13*72 5*50 26 5*72 1*26 1*50 0*85 0*85 1*05 4*95 9-00 4-90 27 1*25 1*27 1-86 3*35 2*55 2*70 1*25 1*90 1*25 28 2*22 2*54 3*00 2*28 2*80 3*25 6*25 11*60 6*10 29 2*78 1*90 2-50 2*13 2*20 2*90 2*10 2*85 2*15 1*41 1*55 2*15 1*42 2*55 2*70 2*15 3*40 2*40 31 2*47 4*50 4*57 3*75 4*40 2*35 315 2*45 July 48-67 61*23 52*50 102*1411 63*00 June 23*37 25*56 28*54 46*60 26*71 Totals 72*04 74*50 69*89 68*45 86-79 81*04 148*74 79*71 It is seen that in June the fall of rain varied from 19*46 in. at Bycalla to 46*60 in. at the flagstaff at Parell, and in July from 46*55 in. on the Esplanade to 102*14 in. at the flagstaff at Parell ; or omitting this as a doubtful return, to 61*23 in. at Airy Cottage, Mazagon ; and the total of the two months varies from 68*15 in. to 86*79 (omitting the gauge at the Parell flagstaff) at Airy Cottage. I do not know whether the investigations were carried out for a whole monsoon, but in case the discre- pancies continued, it would be diflicult to determine the normal fall of rain in Bom- bay. But the anomaly is not confined to Bombay ; Dr. Murkay, in a paper published in the Journal of the Physical Society of Bombay, No. 9, p. 172, has the following ♦ Gauge overflowed. t No register kept for first thirteen days — 4 inches set down at guess. t Gauge overflowed. $ The gauge was running over, but this seei|||» pretty nearly all that fell. It poured in torrents from 5 p.m. on the 25th till 6 a.m. 26th. li The difference here is the same as last month (twice as much of fall being set down here as fell everywhere else) ; and so enormous and unaccountable as to lead to the inference of some tremendous blunder. MDCCCL. 2 Z 354 LIEUT.-COLONEL SYKESES DISCUSSION OF METEOROLOGICAL observations respecting the fall of rain in the town of Sattarah and military canton* ment adjoining : The quantity of rain in the town of Sattarah usually exceeds that in the cantonment, situated a mile N.E., by 6 or 8 inches/' Annexed are the results, to which he has added the fall at his own bungalow or house, equidistant between the town and cantonment, so that the three localities are within the range of a mile. 1 Years. 1844. 1845. 1846. 1847. 1848. 36-06 44-89 40-^4 38*34 42*92 39*52 31*65 43*17 40*98 39*00 33-41 e7‘8i 39-36 The increased fall of rain in the town of Sattarah, which is 2320 feet above the sea-level, is no doubt chiefly caused by the hill, 3200 feet above the sea-level, upon which the fort is situated, rising from the back of the town ; but this will not account for the difference in the fall at the Bungalow and Cantonment Hospital. The facts show how necessary is a local knowledge of physical features before generalizations can be ventured upon safely. In my former paper in the Philosophical Transactions I pointed out the remark- able differences in the fall of rain, twenty to twenty-five years ago on the sea coast, at the top of the Gh&ts, and at Poona, thirty-five miles to the eastward of the Gh&ts. Dr. Murray confirms ray views in a much more detailed manner than I was enabled to attempt, in the following Table for the year 1848 : — Bombay. Ohata. 1 Western Dtetnets. Eastern distrieto. | Moani of 33 yean. Meera. Enteib- wor. Sattorob. Shore. Wye. Plml. tun. Jbutt. nva- poor. Pnnder- pour. Akal. kote. 8anat»> num, meons 14 yean. Sindola, 1848. HiU Fort. Town. Canton. ment. January Febnu^ March April 1 May June July August September ... October November ... December ... 22-26 25-04 17-08 11-25 1-19 0*06 0-20 0-15 1*31 3- 31 46-53 92-) 0 72-33 81-32 4- 58 2-07 0-05 3*60 41-70 74-28 47-81 617 7-23 4-37 2-75 10-93 22-90 616 2-30 2-75 1-85 2-60 5-98 19-83 602 1-80; 2-27 0-19 2*50 4- 10 18-77 5- 00 1- 46 4-64 2- 91 0*80 0- 74 8-04 3*71 14-64 2-60 214 4*89 1- 57 0-04 0- 76 2*79 8-26 12-02 2- 55 1- 40 3- 28 1-71 2-10 2-37 13-20 5-19 1 0- 91 1- 50 4-15 2-09 2-20 9*05 1- 6I 096 275 2- 25 6-24 4-30 2-70 1-24 3-66 2*45 3-59 1- 59 3- 07 4- 82 264 888 2- 17 1 H 1- 83 3*68 4*65 4- 88 2- 84 5- 82 2-80 Year 76-82 254-05 185*16 1 49-64 38*69 39-38 33-41 27-81 20-42 1 20-73 24-18 18-17 25*42 28-55 25-45 With the exception of Bombay and the Sanatarium at Mahabuleshwur, the records are for the year 1848. The following are the respective elevations of the places above the sea-level : — MahabU' leabwor. Sindola. Meera. Entesh- war. Sattarah Fort. Sattarah Town. Sattarah Canton* ment. Bhore. Wye. Pbultun. Jbutt. poor. Funder- poor. Akal- kote. 4500 R340 3700 3200 2320 2320 2350? 2320? 20007 2000? 2000? OBSEaVATlONS TAKEN IN INDIA. 355 Dr. Murray adds, "The prodigious mflnence of the Gh5ts in modifying the amount of the S.W. monsoon rain, is perhaps nowhere more strikingly shown than in the N.W. parts of the Sattarah territory. If we ditiw a line nearly straight from west to east, from Mahabuleshwur, on the summit of the Gh&ts, to Phultun, a distance of little more than forty miles, we shall find at the commencement of the line a rain-fall of 240 inches, at an altitude of 4500 feet ; 180 inches at Sindola, a mile distant, and elevated 4600 feet ; 50 inches at Paunchgunnee, at a further distance of eleven miles and an elevation of 4000 feet ; 25 inches at Wye, four miles further east and 2300 feet in height above the sea, while at the extremity of the line at Phultun, thirty miles from Sattarah, and about the same level as Wye, the quantity is reduced to 7 or 8 inches.” But Dr. Murray must have meant during the S.W. monsoon, as he bad previously represented the fall of rain at Phultun at 24*18 in. in 1848, in' 1847 at 24*04 in., and in 1846 at 18*09 in. Some inches of those amounts however are attributable to the Madras monsoon, which commences in October, when the Malabar coast monsoon terminates, and Phultun, from its easterly position, gets an uncertain sprinkling from the Madras side. Dr. Murray, with a view to show not only the discrepancies in the total annual fall of rain at places within comparatively limited distances situated on the plateau of the Deccan, but the remarkable contrasts in the monthly fall at two proximate places, has given the following Table of the fall of rain at Sattarah and Phultun for 1846 and 1847, Phultun being thirty miles east of Sattarah : — Sattarah. || Phultun. 1 1846. 1847. 1 1846. 1847. January 0-18 1 ( February 0*18 i 0*02 March 0*18 1 0*52 April 10*88 1 1*44 4*19 May 3*49 0*39 ! 1*06 2*88 June 10*49 3*77 1 3*80 1*53 July 16*04 6*28 1-95 0'84 August J2-13 2*68 ! 0-50 September 0*77 3*55 j 1 1*05 S-00 October 2*98 5*25 2*50 3*06 November 0*98 8*00 5*04 4*60 December 2*46 0*05 1*53 0-89 Year 39*52 40*98 18*09 24*04 Dr. Murray, in a paper published in the autumn Number of the Journal of the Physical Society of Bombay for 1849, adds to the proofs of the extraordinary discre- pancies in the fall of rain in proximate localities. He states (page 18), "At the Sana- tnriqm at Mababuleshwnr, at 4500 feet, the rain-fall during 1848 was 245 inches, being within 3 inches of the average fall during the preceding twenty years. At Sindola, the residence of Mr. Prbre (the British minister), situated a mile east from 2 z 2 S56 LI£UT.-COliONEIi SYKES'S DISCUSSION OF MfiTEOROLOGIGAL the Sanatarimn, about 100 feet higher^ with the intervening eminence of Mount Char- lotte rising to a further height of 100 feet, the quantity of rain did not exc^eed 185 inches daring the same period ; hence a difierence of 60 inches or 24 per cent, at two houses situated at the same station. The position of the ground explains the difference, but probably few people, on examining the localities, would have antici- pated its amount. It shows the supreme importance of instituting multiplied obser- vations, before deciding on the site of a sanitary hill station.** To add to the means of comparison, some other rain-fall localities from the sea- coast, and Konkun, or country between the Gh&ts and the sea, — from the Gh&ts and from the plateau of the Deccan, are annexed, being the mean fall for the years 1844-47. Sea*ooMt of Kookun. Konkun, aomewhat lalaad. Western Gh&ts. Western Ohftts, East branch. 1 Deeean. Bombay, «ea-Icvei. Rutna- gberry, 150 feet. Tanna, kvel. Dapoolee, 000 feet. Kundalla, 1740 feet, 183H and 1835. Mahabu- leshwur, 4500 feet. Pauneh- gunnee, 4000 feet, 18:«5, 181V and 1843. Satta- rah, £130 feet. Kola- rs';: Poona, )84‘i feet. Nassick. Bcl- gaum. SOfM) feet. Dbar- war. Ahmcd- nugger, 1000 feet. KhoU- poor, 1847 6873 114*55 134*96 141*59 354*84 50*69 39*30 30*74 19*03 26*72 40*90 38*81 21*83 32*16 Tanna and Dapoolee are situated between the sea-coast and the foot of the Gh&ts. Kundalla is on the crest of the Gh&ts on the high road from Bombay to Poona. The places in the Deccan lie eastward of the Gh&ts. Arranging the above places accord- ing to their supply of rain, it appears the greatest fall is on the crest of the Gh&ts, increasing from 141 ’59 inches at Kundalla at 1740 feet to a mean fall of 254*84 inches at Mahabuiesbwur, at 4500 feet. From the crest of the Gh5ts the supply of rain decreases towards the sea-coast westward, but decreases in an infinitely greater ratio eastward on the plateau of the Deccan. Along the coast the supply of rain diminishes with the increase in latitude. In further illustration of the unequal fall of rain in the Bombay Presidency, the returns for May, June and July 1849 are annexed. They are the latest I have re- ceived except from Bombay. |H|||||||H Surat. Nassick. Asseei^hur. Ahmedabad. Phoonda Gh6t. Mahabu- leahwur. Paunch* gunnee. Calcntu. May June July 0*00 22*82 51*68 0*405 9*056 6*425 ■ Roy 0*00 8*63 7*03 0*23 5*45 16*31 2*03 4*10 7*62 0*00 50*00 83*00 0*00 59*90 89*^4 6*00 13*0 8*25 Total 74*60 15*885 21*99 13*76 11*95 OBSERVATIONS TAKEN IN INDIA. 