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XXVIII. 
ON A NEW FORM OF EQUATORIAL MOUNTING FOR 
MONSTER REFLECTING TELESCOPES. By SIR 
HOWARD GRUBB, M.A.I., F.R.S.; Vice-President, Royal 
Dublin Society. 
[Read Fzpruary 21; received for publication Frpruary 23 ; published Apriu 13, 
1894.] 
Tue problem of mounting large reflecting telescopes satisfactorily 
does not appear so near to solution in this year 1894 as might be 
expected, considering the great strides which have been made in 
mechanical engineering within the last quarter of a century. 
It is now about half a century since the late Karl of Rosse 
mounted a 6-foot reflecting telescope, which has never yet been 
exceeded in size, and for many years, from 1868 to 1888, the 
Melbourne reflector (4 feet) was the largest equatorially mounted 
instrument in existence. 
It is only within the last five years that this has been exceeded 
by Dr. Common’s 5-foot reflector ; and in a recent paper by Dr. 
Common on the mounting of monster reflectors (Monthly Notices, 
Royal Astronomical Society, vol. liii., p. 19), he proposes to revert 
to the old alt-azimuth form of mounting on the ground of the 
immense size and weight (and consequent cost) of an equatorial 
that would be sufficient to carry the great weight of such a 
telescope. 
Now, when we consider that the lowest magnifying power of 
an 8-foot reflector is about 480, and of a 10-foot (such as is pro- 
posed for the Paris (1900) Exhibition) 600, it will be understood 
how very unsatisfactory such a mounting would be for large-size 
telescopes. 
To view objects in a telescope satisfactorily, it is necessary to 
bring them into or near the centre of the field of view, but even 
suppose we are satisfied to view them while in any part of the 
field of an ordinary eye-piece, the object could only be viewed 
in the 8-foot telescope for about 15 seconds, and in the 10-foot 
