12 Mr. Howarp Gruss on Great Telescopes of the Future. 
securing the advantages of silvered glass mirrors without their corresponding 
disadvantages. 
I am not as yet in a position to disclose the exact nature of the improvement by 
which this is effected, but I have reason to believe from experiments that I have 
made, that we shall be able in some little time to produce metallic mirrors with 
a reflective power of at least 25 per cent. over those formerly made. 
Should this result be attained, it will reduce the size of Reflectors of corre- 
sponding power to considerably less than before stated, and modify the several 
advantages of Refractors mentioned above to a considerable extent. 
With respect to the mounting of very large telescopes, I have had so much to say 
on the optical part that I wish to make any remark on the mounting as short as 
possible. Suffice it to say, that I do not see any insuperable difficulties in the 
mounting of such telescopes as we have here been treating of on equatorials similar 
in principle to those we use at present, taking the Vienna as a type of Refractor 
mountings, and the Melbourne as a type of Reflector mountings—subject, of course, 
to modifications necessarily entailed by the increase of weight; and as I am, and 
always have been, a strong advocate for making the observer as comfortable as 
possible (believing that thereby his capacity for useful work will be increased), I 
would strongly advocate in very large telescopes that hydraulic power be utilized 
for conducting all the laborious operations, so that the observer, without moving 
from his chair, might, by simply pressing one or other of a few electrical buttons, 
cause the telescope to move round in right ascension or declination, the dome to 
revolve, the shutters to open, and the clock to be wound. This is no mere Utopian 
idea. Such things are done, and in common use in many of our great engineering 
establishments, and it is only in the application that there would be any difficulty 
encountered. ‘ 
And now, in conclusion, I would say that I have endeavoured to discuss all the 
various points of superiority of each kind of instrument over the other as they 
have occurred to me, and I do not think any more of importance will be found ; and 
I expect it will be seen, that I have done so without advocacy of any particular 
form, but with a desire that the relative weight of all their advantages and disad- 
vantages should be appreciated. 
If any present have followed my reasoning they will probably come to the 
conclusion that no one kind of telescope is best for all kinds of work, and that in the 
choice of telescopes reference must be made to the work the instrument is 
intended for, its geographical and even political position, and many other matters 
which it would not be possible to discuss in a scientific paper. 
