Todd— Untried Form of Mounting for a Telescope. 461 



Tube, objective, and guy-rods are all counterpoised by 

 means of permanent weights on the interior of the sphere, 

 adjacent to the self-adjusting observer's platform (not shown). 

 An objective weighing a ton is counterpoised by a mass of 

 three tons. The mirror for a great reflecting telescope might 

 form the counterpoise. 



When not in use the sphere 

 is revolved until the exterior 

 tube comes down to a nearly 

 horizontal position, and the 

 objective is weather-proofed 

 underneath a removable roof 

 (not shown), something like that 

 of a transit-room. The objec- 

 tive is then accessible in all 

 weathers, for adjustment or 

 other requisite service. With 

 the tube in this position, the 

 observer and his assistant enter 

 the sphere through a door in the 

 tube close to its juncture with 

 the sphere itself. They walk 

 along an internal trottoir, till 

 they reach the adjustable plat- 

 form. This is maintained 

 always charged with its maxi- 

 mum load ; if additional ob- 

 servers go in, their equivalent 

 weight is removed from the 

 platform, and deposited outside 

 the sphere before observations 

 begin. In this way, the sphere 

 is kept submerged to a constant depth — a requisite, the design 

 of which will be apparent farther on. From this platform and 

 out through the opening extends an electrical cable, with per- 

 haps twenty independent circuits, each of which controls an 

 exterior automatic apparatus, whose action very readily gives 

 to the sphere any rapid motion that may be desired, as follows : 



(1) In altitude. 



(2) In azimuth. 



(3) In declination. 



(4) In right ascension. 



These motions suffice for any necessary pointing of the 

 telescope. I need not here go into the details of these auto- 

 matic mechanisms further than to say, that the specified 

 motions may be obtained by means of rubber-faced wheels, 

 strongly mounted in swinging forks or levers (fig. 2), and 



