168 ANNUAL OF SCIENTIFIC DISCOVERY. 



showed, in bright daylight, the stereoscopic relief with blue and red 

 edges, one declared that he saw only the drawing with blue lines, as 

 through the red glass he could see nothing whatever. The eyes of 

 this individual in bright daylight, were in the same condition as a pair 

 of normal eyes by twilight. LoncL, Ed., $ Dub. Mag., June 1852. 



THE BINOCULAR MICROSCOPE. 



At the session of the Physico-Medical Society of New Orleans, 

 April, 1853, Prof. Riddell, the original inventor of the binocular 

 microscope, exhibited and explained a simplification of that important 

 instrument, by which, at an expense not necessarily exceeding thirty 

 or forty dollars, it is practicable, in existing compound microscopes of 

 the ordinary forms, to replace the brass tube carrying the ocular and 

 objective, by an efficient arrangement for binocular vision. To 

 accomplish an equal division of the pencil of light immediately behind 

 the objective, and so effect its distribution to each ocular, only two glass 

 prisms need be used. They must be of such form, that the faces, at which 

 the light is imniergent and emergent, shall form equal angles with the 

 face on which the internal reflection occurs. The chromatic dispersion 

 is a minimum, and really nothing, when these angles are each near 

 eighty-seven degrees. This form is theoretically preferable. In the 

 instrument constructed, and shown by Prof. Blddell, the French 

 rectangular prisms, such as sold by most opticians, were used, in which 

 the equal angles alluded to, are forty-five degrees. The long sides of 

 these, which are the reflecting surfaces, face each other, and, while 

 the edges next the objective are in contact, the upper edges are 

 adjustable, so as to vary at pleasure the inclination of the prisms to 

 each other. In its transit through these prisms, the light is reflected 

 internally, and undergoes two refractions which are almost mutually 

 compensatory. The result is satisfactory. To produce orthoscopic 

 binocular vision, simple, not erecting eye pieces, are required. 



TRACINGS ON GLASS FOR MICROSCOPIC TEST OBJECTS. 



The tracings executed by M. Nobert, of Prussia, for microscopic 

 test objects, are of the most curious character. The plan adopted by 

 him is to trace on glass ten separate bands at equal distance from each 

 other, each band being composed of parallel lines of some fraction of 

 a Prussian inch apart: in some they are 1-1 000th, and in others only 

 l-4000th of a Prussian inch separated. 



To see these lines at all it is necessary to use a microscope with a 

 magnifying power of 100 diameters; the bands containing the fewest 

 number of lines will then be visible. To distinguish the finer lines it 

 will be necessary to use a magnifying power of 2000, and then the 

 lines which are only 1-4 7000th of an inch apart will be seen as per- 

 fectly traced as the coarser lines. Of all the tests yet found for object- 

 glasses of high power these would seem to be most valuable. These 

 tracings have tended to confirm the imdulatory theory of light, the 



