The One Hundred Inch Reflector on Mount 

 Wilson, California 



By Holdridge Ozro Collins, LL. D. 



It is a subject for comment that the largest telescopes 

 throughout the world have been constructed by the liberality 

 ot" individuals, and perhaps a majority of the greatest dis- 

 coveries, as well in Astronomy as in the other Sciences, have 

 been made by those, working in a private capacity, with their 

 own instruments and in their own observatories, and having 

 no connection with any public institution. 



From Galileo's small objective, with a magnifying power of 

 only 83 diameters, which in January. 1610, first presented to 

 an amazed world the four moons of Jupiter, the list down 

 to the present is a long one. embracing the 18 inch Reflector 

 of Herschel in 1789; the six foot Reflector of Lord Rosse in 

 1815; the five foot Reflector of Dr. Ainslie A. Common in 

 1889; the Lick Equatorial of 36 inches; the Yerkes Equatorial 

 of 10 inches; the HO inch Reflector just completed, and the 

 Snow horizontal Reflector of 21 inches, both on Mt, Wilson, 

 and an innumerable number of powerful instruments with 

 objectives from 12 to 28 inches in diameter, all of which 

 have been constructed and operated without government aid. 



The creation of a perfect achromatic Refractor is much 

 more difficult than that of a Reflector of the same aperture, 

 and it is thought that the limit has been reached in the size 

 of the Refractor objective, owing to the elliptical image 

 resultant from the flexure of a large suspended object glass. 

 The objective of the Refractor constructed for the Paris Expo- 

 sition of 1900, is 50 inches in diameter, but it was found 

 impossible to mount it as an Equatorial, and it was placed 

 horizontally upon piers, objects being reflected into it by 

 mirrors. 



For the Reflector, however, the spucnlum which will give 

 a perfect and sharp definition, can be made much larger than 

 is possible for a practicable Refractor objective of a corre- 

 sponding size. 



Between the years 1660 and 1670, Sir Isaac Newton 

 and James Gregory, working independently, discovered the 

 advantages of the Reflector. 



In the youth of the Reflector, the speculum was made of 

 various alloys of silver, nickel, zinc and arsenic, and later, 

 almost universally of copper and tin. with perhaps a small 

 amount of arsenic to increase the whiteness. This form is 



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