THE MICKOSCOPE. 



37 



in two papers by Professor Airy in the Cambridge Philosophical 

 Transactions, to which we refer the mathematical reader. These 

 investigations apply chiefly to the telescope, where the small 

 pencils of light and great distance of the object exclude con- 

 siderations which become important in the microscope, and 

 which are well pointed out in Mr. Varley's paper before men- 

 tioned. 



Fig. 20. 



Let Fig. 20 represent the Huyghenean eye-piece of a micro- 

 scope; F F and E E being the field-glass and eye-glass, and 

 L M N the two extreme rays of each of the three pencils, eman- 

 ating from the centre and ends of the object, of which, but for 

 the field-glass, a series of colored images would be formed from 

 K II to B B; those near B B being red, those near B B blue, 

 and the intermediate ones green, yellow, and so on, correspond- 

 ing with the colors of the prismatic spectrum, This order of 



