1886.] on Telescoinc Objectives and Mirrors, 431 



inertia, are easily stopped and started, and are consequently well 

 adapted for this work. 



I propose to use four of them : one for the right ascension motion 

 of the instrument, and one for the declination ; one for revolving the 

 dome, and one for raising and lowering the observer himself; but 

 instead of having anything of the nature of a 25-foot chair or scaffold, 

 I propose to make the 70-foot floor of the observatory movable. It 

 is balanced by counterjDoise weights, and raised and lowered at will 

 by the observer. Then the observer can without any effort raise and 

 lower the whole floor, carrying himself and twenty jpeople if desired, 

 to whatever height is most convenient for observation ; and wherever 

 he is observing, he is conscious that he has a 70-foot floor to walk 

 about on, which even in perfect darkness he can do in safety. 



The valves and reversing gear of the water engines are actuated 

 by a piece of mechanism, the motive power of which may be a heavy 

 weight raised into position some time during the previous day by man 

 or water power. By means of a simple electrical contrivance, this 

 piece of machinery itself is under the complete control of the observer, 

 in whatever part of the room he may be, and he carries with him a 

 commutator of a compact and convenient form, with eight keys in 

 four pairs, each pair giving forward and backward movements respec- 

 tively to 



A. Telescope movement in right ascension ; 



B. Telescope movement in declination ; 



C. Eevolution of dome ; 



D. Raising of floor. 



The remaining operation, opening of shutter, is easily effected 

 without any additional complication. 



It is only necessary to anchor the shutter (which moves back 

 horizontally) to a hook in the wall and move the dome in the opposite 

 direction by motion C ; the shutter must of course be opened by this 

 motion. 



It is very possible that there may be some here who have found 

 what I have had to say on the subject of the figuring of objectives very 

 unsatisfactory. They may have expected, naturally enough, that 

 instead of treating of generalities to such a large extent as I have 

 done, I should have given precise directions, by the following of 

 which rigidly any person could make a telescopic objective. 



To those, however, who have followed me in my remarks, the 

 answer to this will probably have already suggested itself. It is the 

 same answer which I give to those who visit my works and ask what 

 the secrets of the process are, or if I am not afraid that visitors will 

 pick up my secrets. All the various processes which I have described 

 up to that of the figuring are I consider purely mechanical processes, 

 the various details of which can be communicated or described as any 

 mechanical process can be ; but in the last final and most important 

 process of all there is something more than this. A person might 

 spend a year or two in optical works where large objectives are made, 



Vol. XI. (No. 80.) 2 f 



