34 



OPTICAL PRINCIPLES OF THE MICROSCOPE. 



equally half -good pictures -which are ohtainahle hy MM. Nachet's 

 original construction, we had in Mr. Wenham's one good and one 

 indifferent picture, the latter would be decidedly preferable. But, 

 in point of fact, the deterioration of the second picture in Mr. 

 Wenham's arrangement is less considerable than that of both 

 pictures in the original arrangement of MM. Nachet ; so that the 

 optical performance of the Wenham Binocular is in every way 

 superior. It has, in addition, these further advantages over the 



Fig. 20. 



Fig. 21. 



Wenham's Stereoscopic Binocular Microscope. 



preceding -.—First, the greater comfort in using it (especially for 

 some length of time together), which results from the convergence of 

 the axes of the Eyes at their usual angle for moderately-near objects ; 

 second, that this Binocular arrangement does not necessitate a 

 special instrument, but may be applied to any Microscope which is 

 capable of carrying the weight of the secondary body ; for the 

 prism is so fixed in a movable frame that it may in a moment be 

 taken out of the tube or replaced therein, so that when it has been 

 removed, the principal body acts in every respect as an ordinary 



