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58 On Microscopes and Microscopy. 



any desirable extent, by the use of Armci's prism, which gives a 

 wider angle than the prism of Nachetj*or any other similar means 

 used. The claim for superiority was soon found to lie between 

 the lenses of Mr. Ross, Mr. Spencer and M.-Nachet. Those of 



the other English makers were not, I was well convinced at the 



time, fair specimens of their skill; and as yon will soon perceive, 

 a subsequent experience justified this view. ,^ / 



With Nobert's lines it was thought that thgre was not a very 

 marked difference between the three lenses above mentioned. 

 At any rate as we could not all see alike, it was not regarded as 

 being any especial test in this case. 



The markings on both the Gramniatophora and Amici's test, 

 could be made out by all three, but certainly most distinctly and 

 sharply defined by Ross and Spencer, — the field of Nachet not 



appearing quite as clear and light. 



Between Ross and Spencer on the test of Amici, there did ap- 

 pear to be but very little difference, although I am free to say 

 that if there was a choice of sharpness of definition, it was in 

 favor of Ross. u 



On the other hand, with the Grammatophor a, the opinion os- 

 cillated as much in favor of Spencer. So that with these two 

 supreme tests, there appeared really to be no particular choice 

 between Spencer and Ross, but as usual in such matters, the 

 owners of the lenses felt no disposition to exchange with each 

 other. 



The working of Nachet's lenses, although they did not come 

 up fairly with those of Ross and Spencer, was most excellent ; 

 and quite remarkable, considering what has hitherto been attained 

 by the French opticians. Their excellence was also perceived 

 in their great focal length, and other fine working qualities to 

 which I shall soon allude. Moreover, although the results ob- 

 tained upon organic particles, such as blood and other corpuscles, 

 were in about the same ratio as the other tests, yet with these 

 especially the lenses of Nachet claimed great credit for their 

 clear achromatic power, representing the color of the particles in 

 as nearly their natural condition fully as finely as any lenses I 

 had before seen. 



The main result of the trial was, in this case, the same in one 

 particular as in other trials I have made, viz., to elevate our opin- 

 ions of the capabilities of the lenses employed, it matters not by 

 whom made. And if it was with much astonishment that the 

 French opticians viewed the lenses of Mr. Spencer, I am sure 

 that it was with no less wonder that some of our countrymen 

 present saw the excellent glasses of Nachet. But to all it must 

 be a cause of greater astonishment and admiration, that one self- 

 educated, and who had had none of the experience of Europe, 

 should make lenses fully equalling those of Europe's best artists 

 who have been educated to the trade froni their earlier days. 





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