236 M. Euler on the Perfection of the Microscope. 



ino- power, the less will be the clearness, and the portion of 

 the object which we can see at once. 



As to the degree of clearness, it will be proper to observe, 

 that, if the magnifying power is under 20 times, the objects 

 will appear with their natural clearness as if we were looking 

 at them with the naked eye. We shall call this degree of na- 

 tural clearness 1 ; and we shall express, in the following table, 

 for each magnifying power, the clearness of the object by the 

 thousand parts of the unit. 



In the same table we shall insert all the diameter of the 

 part of the object, which will be seen at once by each magni- 

 fying power. 



But to judge of the magnifying power, we shall refer it, as 

 is usual, to the distance of eight inches, so that the numbers 

 marked for magnifying power will indicate how many times 

 each object will be seen greater by the microscope than by the 

 naked eye at the distance of eight inches. 



This being settled, the first column A, of the table will 

 mark the magnifying power ; the second B, the distance be- 

 tween the object-glass and the first eye-glass ; the third C, the 

 decree of clearness ; and the fourth D, the diameter of the 

 portion of the object seen by the microscope. 



