ALVAN GRAHAM CLARK. 521 



attention was first called to lens making by an attempt of liis sou George 

 to construct a telescope while a student at Andover. The books repre- 

 sented it as a very difficult thing. However, genius knows no limita- 

 tions, and, without previous knowledge or discipline, the work was 

 commenced and a telescope successfully made in the year 1846. 



The work thus begun soon became a permanent occupation. Painting 

 was exchanged for telescope making, and, about 1850, the house of 

 Alvan Clark and Sons established. Both the sons inherited the father's 

 skill, and entered into the work with him. Upon his death, the business 

 was carried on by the sons together, and, upon the death of George, by 

 Alvan alone. 



Alvan Graham Clark was pre-eminently a self-made man. Inheriting 

 to a reraai'kable degree the talents of his father, and with a fair amount 

 of common school education, he carried lens making to the highest state 

 of perfection the world has ever seen, so that a so called mechanical 

 occupation was transferred to the realm of high art. But to make a 

 good lens, good glass is necessary, and for a time the impossibility of 

 obtaining good disks of large size seemed to present a barrier to the 

 progress of telescope making. Fortunately this has been overcome in 

 recent years by several European makers, notably by Fell of Paris and 

 his successor Mantois, and it was upon this firm that Mr. Clark always 

 relied. 



In fact, disks sent by them were frequently rejected. Sometimes a 

 lens would be nearly completed, and, with the gathering in of the last 

 rays of light, a slight vein would be seen. Invariably the wellnigh 

 completed lens was rejected and days of labor lost, for Mr. Clark would 

 say, " I will keep up the standard of my work," As a result, the 

 exquisite definition and clean cut images always confirmed the high 

 standard of excellence set by the maker. 



To make a lens is by no means an easy task. When one considers 

 that not merely the chromatic and spherical aberration which relate to 

 color and general figure proper have to be regarded, but also roundness, 

 balance of figure, and several other considerations, it becomes evident 

 that to construct a glass of the highest excellence is a very difficult task. 

 To accomplish this, one must have not only a keen eye to see the defects, 

 but good judgment and consummate skill to remove them without the 

 incorporation of others. 



One of the salient features of the Clarks' work was the method of 

 local correction. This, although not wholly new in principle, was early 

 adopted by them, and so extended and specialized that it has been 



