251 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and a"h", each of which will be of the same size as the object. 

 Two compound Microscopes with eye-pieces C and C, and objectives 

 D and D', are then used to examine the two images. 



Professor Harting writing in 1858 said " were the images a' b' 

 and a" b" so clear and sharp that they might be assumed to repre- 

 sent the object itself, objectives of short focal length might be used. 

 But we are yet far from having the objects so represented by our 

 present lenses. Even if the images are formed by objectives of fairly 

 low power — 1 to 2 cm. — the difference between the images and the 



Fto. R3. 



object is still too great, as was found as the result of some experi- 

 ments made for the purpose. This contrivance cannot therefore be 

 applied successfully to the construction of binocular Microscopes, 

 which is the more to be regretted as this arrangement seems to 

 satisfy better than any other the requirements of true stereoscopic 

 vision. Perhaps future improvements in the construction of objec- 

 tives will more readily allow of the accomplishment of the desired 

 aim." 



As this was written nearly thirty years ago, it is very probable 

 that the defects in the objectives which were then found to mar the 

 action of the suggested instrument would not now be met with, but we 

 doubt nevertheless if it would be found at all worth while to construct 

 such an instrument. Any improvement in the stereoscopic effect over 



