The Binocular Microscope. By F. Jentzsch. 7 



length of time, principally owing to the fatigue of the muscles of 

 the eye. Nevertheless, this method of construction for stereoscopic 

 purposes is defensible at least in one respect, inasmuch as the pur- 

 pose is to assist the purely optical effect by adding auxiliary 

 psychological perceptions, in this case by convergence. For a 

 purely binocular instrument, on the other hand, convergence of the 

 optical axes of the eyes loses all its importance. We would rather 

 require each eye to work as far as possible without effort of accom- 

 modation, that is without strain, and that the point of convergence 



Fig 2. 



of the axes of the two eyes should be as distant as possible : in other 

 words we prefer to place the two eye-pieces parallel. 



With this arrangement everyone * can succeed in making the 

 two images coincide, and this is accomplished the sooner the more 

 effectually one avoids any sort of strain in working. If the coinci- 

 dence of the images takes place under conditions of complete re- 

 laxation, the tranquillity and steadiness of the image is surprising. 

 The distance at which the image is located varies in individual 

 cases as with the ordinary Microscope. 



* It is a fact that anyone, who can see at all with both eyes, can use any 

 properly designed and well-constructed binocular Microscope without previous 

 practice. 



