None
244. If the resistance of 1 mile of wire 2™"* in diameter is 4.72 ohms, what is the resistance of 3 miles of wire of the same material 3™"^ in diameter ? 245. What length of* copper wire -1™™ in diameter has the same resistance as 720™ of copper wire 4"™ in diameter ? 246. The conductivity of iron is \ that of copper. If the resistance of a copper wire 1 mile long and \ in. in diameter is 6.8 ohms, what is the resistance of an iron wire ^ in. in diameter and 5 miles long? 247. If 50 volts force 54.8 amperes of electrical current through a lamp, what is the resistance ? 248. If the resistance of an electric lamp is 2.8 ohms when, a current of 10 amperes is passing through it, what is the voltage ? 249. Five arc lamps on a circuit have each a resistance of 2.35 ohms. The resistance of the wires is 1.2 ohms and of the dynamo is 0.75 ohm. What voltage is required to send a current of 15 amperes through the circuit ? TABLES. 399 TaJ)l6 of Specific Gravities. NAME OF SUBSTANCE. Acid, acetic, strongest .. ** nitric, " .. ** sulphuric, ** .. Air Alcohol, pure ** of commerce .. Aluminum, lightest . .. Brass, average Brick, common .... ** pressed Cedar, dry Cherry, dry, average . .. Coal, bituminous, average. " anthracite, . . .. Copper, cast VyOxK ■••••... Glass, average Gold, pure, cast .... Granite, average .... Gypsum, heaviest .... Hydrogen Ice Iron, cast, average . .. '* wrought, average .. Lead, cast ** white Lignum vitsa Lime Marble, average .... Mercury Milk Nitrogen Oil, linseed Oak, dry white .... Oxygen Pine, dry white .... Platinum, hammered .. Salt Sand, average Silver, hammered .... Slate, lightest Tin, cast Water, sea Zinc SPECIFIC QBAVITY. 1.062 1.583 1.841 0.001292 0.792 0.834 2.560 7.611 2.000 2.400 0.350 to 0.600 0.716 1.250 1.500 8.788 0.240 2.760 19.258 2.720 2.288 0.0000893 0.930 7.150 7.770 11.350 7.235 1.333 0.804 2.720 13.580 1.032 0.001250 0.940 0.830 0.001429 0.400 21.841 2.130 1.650 10.500 2.110 7.816 7.291 1.026 7.190 WEIGHT OF CUBIC FOOT IN POUNDS. 66.4 • 98.94 115. 0.0808 49.43 52.1 160. 475.7 125. 150. 22 to 37.5 44.7 78.1 93.75 549.3 15. 172.5 1204. 170. 143. 0.00558 68.1 447. 486. 709.4 452. 83.3 50.26 170. 849. 64.6 0.0781 58.8 51.9 0:0893 25. 1365. 133. 103. 656.2 132. 488.5 456. 64.13 449.4 400 TABLES. Table of Selected Constants, 00 H O Q iz;. ^H (4 » H H>W M u CQ CQ O OD Eh P3 CONSTANT. Diagonal of square in terms of side Side in terms of diagonal . .. Cube root of 2 Cube root of -J- Square root of 20 Square root of 3 ...... Square root of i^ Square root of 30 Square root of 6 Extreme and mean ratio . .. Extreme and mean ratio . .. Circumference in terms of diameter Diameter in terms of circumference Circle in terms of diameter square Square in terms of the circle .. Sphere in terms of diameter cube Cube in terms of sphere .... One meter in feet . .. One foot in meters .. One meter in yards .. One yard in meters .. One centimeter in inches One inch in centimeters. One mile in kilometers. One kilometer in miles. One square foot in square meters One square meter in square feet. One sq. inch in square centimeters One square centimeter in sq. inches One acre in hektars One hektar in acres One cubic foot in cubic centimeters One cubic meter in cubic feet .. One U. S. bushel in cubic inches. One U.S. bushel in cu. centimeters One cubic foot in U.S. bushels One U.S. gallon in liters . .. One liter in U.S. gallons . .. One gram in grains. One grain in grams. One pound in kilograms One kilogram in pounds NUMBER. 1.4142136 0.7071068 1.2699210 0.7937002 4.4721359 1.7320508 0.5773503 5.4772256 2.2360680 0.3819660 0.6180340 3.1415927 0.3183099 0.7853982 1.2732395 0.5235988 1.9091406 3.2808693 0.3047973 1.0936231 0.9143918 0.3937043 2.5399772 1.6093295 0.6213768 0.0929014 10.7641036 6.4514847 0.16500308 0.4046784 2.4710982 28,316.085 35.315617 2150.42 35,2.38.117 0.8035640 3.7853103 0.2641791 15.4323487 0.0647990 0.4535927 2.2046212 LOGABITHM. 0.1506150 9.8494850 0.1003433 9.8996567 0.6505150 0.2386606 9.7614394 0.7386606 0.3994860 9.6820247 9.7910124 0.4971499 9.5028501 9.8960899 0.1049101 9.7189986 0.2810014 0.5159889 9.4840111 0.0388677 9.9611323 9.6951702 0.4048298 0.2066460 9.7933550 8.9680221 1.0319779 0.8096596 9.1903404 9.6071100 0.3928900 4.4520332 1.5479668 3.3325232 4.5470127 9.9050204 0.6781015 9.4218985 1.1884320 8.8116680 9.6666660 0.3433340. 