430 Mr, Howard Gruhh [April 2, 



more favourable conditions for work than any other large telescope 

 in the world. 



The 36-inch objective is at present in process of construction by 

 the Messrs. Clark of America, but the mounting has not yet been 

 contracted for. 



Some years since, in a paper published in the Transactions of the 

 Royal Dublin Society, I shadowed forth a principle which I con- 

 sidered should be adopted in great telescopes of the future. The 

 trustees of the Lick observatory having invited me to design an 

 instrument for the 36-inch objective, I have put into practical form what 

 I had before given but general principles of, and the design which this 

 model illustrates is the result. 



Whether this design will ever be carried out or not I cannot tell, 

 but even as a proposal I trust it may be interesting enough to excuse 

 my introducing it (somewhat irrelevantly perhaps) to your notice 

 to-night. 



The design includes the equatorial itself, with its observatory, 

 dome, and provision for enabling the observer to reach the eye end 

 conveniently. 



The conditions I laid down for myself in designing this observa- 

 tory were that it would be possible for the observer single-handed to 

 enter the equatorial room at any time, and that, without using more 

 physical exertion than is necessary for working the smallest-sized 

 telescope, or even a table microscope, he should be able to open the 

 70-foot dome, turn it round backwards and forwards, point the equa- 

 torial to any part of the heavens, revolving it in right ascension and 

 declination to any extent, and finally (the most difficult of all) to 

 bring his own person into a convenient position for observing. I say 

 this last is the most difficult of all, for I think any who have worked 

 with larger instruments will allow that there is generally far more 

 trouble in moving the observatory chair (so called) and placing it in 

 proper position than in pointing the instrument itself. In this 

 instrument the " chair " would require to be 25 feet high, and with 

 its movable platform, ladder, balance-weight, &c., would weigh 

 probably some tons. Even if very perfect arrangements were made 

 for the working of this chair, the mere fact that the observer while 

 attempting to make the most delicate observations is perched upon a 

 small and very unprotected platform 25 feet above the floor and in 

 perfect darkness, tends to reduce his value as an observer to an extent 

 only to be appreciated by those who have tried it. 



No matter how enthusiastic a man may be at his work, I would not 

 put a high value on his determinations if made while in a position 

 which calls for constant anxiety for his own personal safety. I would 

 go even further still, and say that even personal comforts or discomforts 

 have much to do with tho value of observations. 



I propose, therefore, that all the various motions should be effected 

 by water power. There are water engines of various forms now 

 made, some of which have no dead point, and having little vis 



