- ASTRONOMY AND METEOROLOGY. 285 



grounds, communicating with his workshop, is an original con- 

 trivance for providing a fictitious star, for converting day into 

 night, so that he may examine and repolish at any hour; it also 

 provides a sufficient space filled with homogeneous air, much bet- 

 ter adapted for nice observations than the external atmosphere. 

 All this is what is meant by Mr. Clark's method of local connection, 

 for which the Rumford premium was awarded. The late Mr. 

 Fitz, of New York, also used a method of local correction. But 

 he retouched only one surface of his compound lens, and was 

 therefore obliged to leave it with such irregularities as must re- 

 sult from the local working ; as it could not be returned to the 

 tool upon which it was originally polished without rapidly losing 

 all the advantage gained by the local treatment. 



" Whenever Mr. Clark dismounts his lens and retouches it, he 

 separates the component parts, and applies his local correction to 

 each of the four surfaces. These will tend to fall back to the 

 primitive figure ; but, while the elasticity of the tools and the 

 lens together suffice to prevent a very rapid change, under Mr. 

 Clark's skilful and delicate handling, he allows for and guards 

 against this by a slight excess of local working. It is therefore 

 to this nice, artistic handling that our associate's lenses owe, in no 

 small degree, their pre-eminence. 



" The justification of the Academy's award is found in the 

 importance and the originality of this method of local correction. 



" Its importance is assured and measured by the fact that by it 

 a lens of 18 to 20, or even 24 inches aperture is as manageable 

 under construction now, as 9 to 12 or 15 inch lenses lately were 

 without it. Through this invention, and the consummate skill by 

 which it is turned to account, supremacy in this high art, which 

 lingered long in London under the influence of the Dollands, and 

 then deserted its ancient home for Munich, has now confessedly 

 taken up its abode with us, in Mr. Clark's unpretending but most 

 efficient establishment at Cambridge. 



"The originality of the invention will hardly be questioned 

 when it is known that Foucault, as recently as 1858, tried some- 

 thing of the same kind on the single surface of a 'reflector, with 

 fine results, and then suggested its application to lenses, in honest 

 ignorance that this was what Mr. Clark had been doing for 10 

 years, and in the most delicate and refined way. 



" In the administration of Count Rumford's trust, the Academy 

 could take notice only of such work as comes within its specific 

 terms, and could adjudge his premium solely in regard to the ab- 

 solute merit of some particular invention. It could take no ac- 

 count of the difficulties and disadvantages under which Mr. Clark 

 has struggled on, without early scientific training, without 

 access to any of the gathered experience which is handed down in 

 optical workshops, without having seen before any, even the 

 commonest, process which he had to execute, with little means 

 of knowing what had already been done, much less how it had 

 been done, without even encouragement, until after success 

 achieved made encouragement superfluous, earning by daily 

 toil in one fine art the moans and opportunity of developing his 



