in fig1 a well drilling rig which is in most respects conventional and includes the usual upwardly projecting derrick or mast 11 from which a drill string 12 is suspended by a block and tackle assembly 121 including a crown block 13 and a traveling block 14 suspended from the crown block by a line 15 the drawworks 16 actuates line 15 to move the traveling block and drill string upwardly and downwardly along a vertical axis 18 the string is formed of a series of tubular pipe sections 19 threadedly interconnected in end to end relation at joints 20 it is contemplated that for purposes of the present invention the apparatus may either be of a type in which the entire string is rotated by a rotary table 21 mounted on the rig floor 22 or of a type in which the string is stationary and only the bit 23 at its lower end rotates fig1 typically illustrates the latter arrangement with the lowermost section 24 of the drill string containing a motor 25 of known type adapted to be driven by the pressure of drilling fluid circulated downwardly through the drill string to turn bit 23 about axis 18 for progressively drilling well 26 as the string.