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NOTES ON A PAPER RECENTLY PUBLISHED IN THE 
ASTROPHYSICAL JOURNAL, by PROFESSOR E. HALE, 
of the Yerkes Observatory, Chicago, on “THE COMPARATIVE 
VALUES OF REFRACTING AND REFLECTING TELE- 
SCOPES FOR ASTROPHYSICAL OBSERVATIONS.” By 
SIR HOWARD GRUBB, F.R.S., Vice-President, R. D. 8. 
[Read May 19; Received for Publication May 21 ; Published SepremBer 14, 1897.] 
THe very first memoir in the first volume of the Transactions 
of the Royal Dublin. Society (New Series, 1877), was a Paper 
by the author on “ Great Telescopes of the Future.” That Paper 
was written at a somewhat critical period in the history of large 
telescopes, and was intended to draw attention to several advan- 
tages which reflecting telescopes possessed, more particularly for 
spectroscopic and certain lines of physical work, which advantages, 
in the opinion of the author, rendered it probable that the great 
telescope of the future would be of the reflecting and not of the 
refracting type. _ 
Glancing back for a moment over the past history of tele- 
scopes, it will be remembered that the development of the reflect- 
ing telescope got its first impetus from the failure of Sir Isaac 
Newton to achromatize telescopic objectives. Hven after “ Dolland ” 
-had perfected his great invention of the achromatic objective, re- 
-flectors were in considerable favour on account of the difficulty of 
procuring perfect pieces of optical glass, but as this difficulty 
decreased the reflecting telescope, then always made with metallic 
‘mirrors, gradually lost ground on account of the difficulty of 
renewing the optical surface when tarnished. 
1Vol. 5, No. 2, Feb. 1897. 
