M. Euler on the Perfection of the Microscope. 237 



A B CD 



900 28,125 0,022 0,004 



1000 41,250 0,020 0,004 



1200 37,500 0,016 0,003 



1400 43,750 0,014 0,003 



1600 50,000 0,013 0,003 



1800 56,250 0,011 0,002 



2000 62,500 0,010 0,002 



2500 78,125 0,008 0,002 



3000 93,750 0,007 0,001 



As for the degree of clearness, we must also observe, it is 

 not absolutely proportional to the numbers C in the table, but 

 more to the square of these numbers, so that the clearness de- 

 creases much more than it is marked in the table. If you wish 

 to magnify one thousand times, the degrees of clearness is not 

 Jo of the natural clearness, but only j/^, but that degree of 

 clearness is still pretty great in comparing it to the clearness 

 of the full moon, which cannot exceed 2 5/000 °f tnat °f tne 

 sun ; from which we see that the degree of clearness which 

 corresponds to a magnifying power of 100 is still ten times 

 greater than the clearness of the full moon, which will be suf- 

 ficient for the objects we may wish to examine. 



If we wished, however, to increase the magnifying power, 

 we must illuminate the objects as we do when we employ the 

 common microscopes; but it will not be necessary to go farther, 

 because it is probable that a magnifying power of 300 or 400 

 times, which represents the objects distinctly, will discover a 

 great deal more than the common microscopes with a magni- 

 fying power of some thousand times. 



N. B. — This article is an extract from a work published at 

 Petersburg in 1774, under the title of Detailed Instructions 

 to bring Telescopes of different kinds to the highest degree of 

 perfection of which they are susceptible, deduced from the Diop- 

 tric Theory of Leonard Euler, and written in a way to assist 

 workmen, by Nicolas Fuss; with the Description of a Micro- 

 scope of the most perfect kind, capable of every degree of 

 magnifying power. Article 7, p. 75 to 83. 



