sachet's double-bodied microscope. 87 



pencil of rays issuing from the object-glass by a separating^Prisni 

 placed in its course, first introduced for the production of Stereo- 



Fig. 44. 



Nachet's Double-bodied Microscope. 



scopic eeffcts (§§ 26-29), has been applied by MM. Nachet to 

 another purpose, — that of enabling two or more observers to look 

 at the same object at once, which is often a matter not only of 

 considerable convenience, but also of great importance, especially 

 in the demonstration of dissections. The instrument, as arranged 

 for this purpose, is shown in Fig. 44. MM. Nachet have also devised 

 another arrangement, by which the form of the separating Prism 

 is adapted to divide the pencil into three or even into four parts, 

 each of which may be directed into a different body, so as to 

 give to several observers at one time a nearly identical image of 

 the same object. Of course, the larger the number of secondary 

 pencils into which the primary pencil is thus divided, the smaller 

 will be the share of light which each observer will receive ; but 

 this reduction does not interfere with the distinctness of the 

 image, and may be in some degree compensated by a greater in- 

 tensity of illumination.* 



62. Powell and LealanoVs Non-Stereoscopic Binocular. — The 

 great comfort which is experienced by the Microscopist from the 

 conjoint use of both Eyes, has led to the invention of more than 

 one arrangement by which this comfort can be secured, when those 

 high powers are required, which cannot be employed with the 



* The price of the Double-bodied Microscope, with three Objectives, is 

 300 francs, or about £12. 



