36 



THE MICROSCOPE. 



sisting of the field-glass F F, and 

 the eye-glass E E, forming together 

 the modern achromatic microscope. 

 The course of the light is shown by 

 drawing three rays from the centre 

 and three from each end of the ob- 

 ject O. These rays would, if left to 

 themselves, form an image of the 

 object at A A, but being bent and 

 converged by the field-glass F F, 

 they form the image at B B, where a 

 stop is placed to intercept all light 

 except what is required for the for- 

 mation of the image. From B B 

 therefore the rays proceed to the 

 eye-glass exactly as has been de- 

 scribed in reference to the simple 

 microscope and to the compound of 

 two glasses. 



If we stopped here we should con- 

 vey a very imperfect idea of the 

 beautiful series of corrections effect- 

 ed by the eye-piece, and which were 

 first pointed out in detail in a paper 

 on the subject published by Mr. Var- 

 ley in the 51st volume of the Tran- 

 sactions of the Society of Arts. The 

 eye-piece in question was invented 

 by Huyghens for telescopes, with no 

 other view than that of diminishing 

 the spherical aberration by producing 

 the refractions at two glasses instead 

 of one, and of increasing the field 

 of view. It was reserved for Bosco- 

 vich to point out that Huyghens 

 had by this arrangement accidentally 

 corrected a great part of the chrom- 

 atic aberration, and this subject is 

 further investigated with much skill 



u..., 



