Grussp—Lquatorial Mounting for large Reflecting Telescopes. 258 
telescope for 12 secondsat atime. This would render the telescope 
practically useless. 
The larger the telescope the more important it is to have it 
equatorially mounted, and driven correctly by clock-work, so that 
the observer may watch for a favourable opportunity for distinct 
vision. It is to be remembered that, in the case of very large 
apertures, itis only in glimpses on a fine night that good definition 
is to be obtained; and therefore it is all the more important that 
the observer should have the opportunity of watching for, and 
taking advantage of, these favourable moments. 
I am one of those who think that reflectors have not had a 
fair chance in the race with refractors, and I believe a great 
future is before them. I have therefore paid some attention to 
the possibilities of satisfactorily mounting reflecting telescopes of 
what may be called monster sizes—I mean of 8 or 10 feet in 
diameter ;—and as our neighbours in France have announced 
their intention of constructing a 3-metre reflector for the next 
Paris Exhibition of 1900, this may not be an inappropriate time 
to discuss the question. 
The problem to be solved is that of mounting, on an equatorial 
movement, a telescope of, say, 80 or 100 tons weight, so perfectly 
equipoised and relieved of friction that it can be conveniently 
manipulated and carried by clock-work, or some motive power, to 
follow a celestial object with such accuracy that it will not at any 
moment vary from its correct position by a quantity equal to the 
apparent motion of that object in a space of one-tenth or one- 
twentieth part of a second. 
That the problem is one of difficulty is sufficiently evidenced by 
the fact that Dr. Common, who has done the latest and best thing 
in this way, in equatorially mounting his 5-foot reflector, practic- 
ally gives up hope of success, and proposes to revert to the almost 
useless alt-azimuth form. 
I am, however, by no means so despairing, and I believe that 
before long the apparently impossible will become possible, and 
I would venture in this present Paper to shadow forth what I 
believe will be found the most hopeful principle on which to mount 
the monster reflecting telescope. 
Dr. Common himself has made a splendid advance in adopt- 
ing the system of flotation of the polar axis; this principle of 
