A Clepsydra for Driving Telescopes. 



421 



A CLEPSYDRA FOR DRIVING TELESCOPES. 



BY FREDERICK BIRD. 



The instrument of which a sketch is here given was devised by 

 me for the purpose of imparting a slow motion to a silvered 

 glass reflector, twelve inches 

 aperture, mounted equatoreally. 

 The tube is suspended on axes 

 in a rectangular wooden frame, 

 terminating in pivots, one of 

 which rests in a socket em- 

 bedded in stone, and the other 

 drops into a cast-iron Y bearing. 

 The telescope is well balanced 

 in all positions, and moves with 

 great freedom. 



The motive power for driv- 

 ing, or rather drawing the tele- 

 scope, resides in a column of 

 water, containing about one 

 and a half gallons, and placed 

 in a cylindrical vessel, A, of 

 zinc, three feet long, and four 

 inches diameter. On the out- 

 side of this vessel, near the base, 

 is inserted a small gas -tube, 

 three -eights of an inch bore, 

 communicating with the interior. 

 The tube is carried up level with 

 the top, bent sharply round, and 

 brought down again below the 

 base, about six inches, to form a 

 syphon, S. 



Eighteen inches from the 

 end is inserted a stop-cock, T, 

 to regulate the flow of water, 

 and a vessel is placed below to 

 receive it. At the upper end 

 of the long vessel, A, and at- 

 tached to it, is a curved iron 

 bracket, perforated at the back, 

 by which the whole apparatus 

 may be hung upon a nail or 

 hook, C, in any convenient 

 position, if possible, within reach of the observer at the tele- 



