48 CONSTRUCTION OF THE MICROSCOPE. 



as to colour. It is to be observed also, that the images 

 b b and r r are curved in the wrong direction to be dis- 

 tinctly seen by a convex eye-lens, and this is a further 

 defect of the compound microscope of two lenses. But 



Fig. 32. 



the field-glass, at the same time that it bends the rays and 

 converges them to foci at b' b 1 and / r', also reverses the 

 curvature of the images as there shown, and gives them 

 the form best adapted for distinct vision by the eye-glass e e. 

 The field- glass has at the same time brought the blue and 

 red images closer together, so that they are adapted to 



