. Machinery and processes of the industrial arts, and apparatus of the exact sciences. gular prism c, in which it undergoes asecond reflection to correct the reversal produced bythe first, aud emerges in the direction d. The inequal-ity of illumination mentioned as occurring in thebinocular of Powell and Lealand is a consequence ofa too small angle of incidence upon the first reflect-ing surface. In Professor Smiths instrument, the in-clination of the mirror to the incident ray is such as toproduce a sensible equality between the intensities ofthe reflected and transmitted light. An inclinatio
. Machinery and processes of the industrial arts, and apparatus of the exact sciences. gular prism c, in which it undergoes asecond reflection to correct the reversal produced bythe first, aud emerges in the direction d. The inequal-ity of illumination mentioned as occurring in thebinocular of Powell and Lealand is a consequence ofa too small angle of incidence upon the first reflect-ing surface. In Professor Smiths instrument, the in-clination of the mirror to the incident ray is such as toproduce a sensible equality between the intensities ofthe reflected and transmitted light. An inclination ofthe plane of the mirror 80° to the axis of the telescopehas been adopted by Professor Smith, and is found toanswer the purpose. It was the original design ofthe inventor to make the reflector so far wedge-shaped as to throw the reflection from the secondsurface out of the field, but actual experiment showedthat a very slight inclination of the two surfaces toeach other was sufficient to make the two imagescoalesce, at least for a determinate position of the eye-piece, which is. DOUBLE AND TRIPLE MICROSCOPES. 543 Fig. 113. easily found by trial. The only instruments as yet made on this planhave been constructed by Professor Smith with his own hands. Thewriter, by actual experiment, has found the performance to be in a highdegree satisfactory. Mr. Nachet exhibited in the Exposition a binocular dissecting micro-scope of a neat and compact form; and another still simpler was exhib-ited by Mr. J. Beck. The division for purposes of binocularvision of the compound pencil of lightproceeding from the objective, suggestsnaturally the adaptation of the instru-ment to the use of two observers simul-taneously. A double microscope con-structed on this principle by Mr. Cachetis represented in the accompanying fig-ure. It is obvious that, after the divisionof the beam, it is only a matter of mechan-ical detail to give to the parts any direc-tion which may be found most conven-ient. For pu
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