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THE BINOCULAR MICROSCOPE. 



By Edwakd M. Nelson, F.R.M.S. 



{Read October Sth, 1918.) 



Among microscopists there are some who regard the binocular 

 merely as a toy or plaything, while others take it more seriously and 

 consider it an instrument useful in scientific research. The bulk 

 of microscopes in use are, however, monoculars. This no doubt 

 is partly due to the less cost and greater portability of the mono- 

 cular instrument, and partly to the failure of the Wenham and 

 Stephenson binoculars with high-power objectives, which of course 

 means that if high- power work had to be done, one could not get 

 on with a binocular alone, a monocular would have to be added 

 to the outfit ; the purchase of two microscopes instead of only a 

 monocular would necessarily deter many from even thinking of 

 l>uying such " a useless plaything as a binocular." 



A pertinent question has been asked, " What discoveries have 

 been made with a binocular ? " It must be admitted that so far 

 it is difficult to point to any. Before this note is finished we trust 

 that a satisfactory answer will, for the first time, have been found 

 to that question, first asked byHooke 250 years ago. To proceed 

 to our investigations, let us take the Greenough as our standard 

 instrument. It consists, as you are all aware, of two erecting 

 microscopes inclined to one another at the normal inclination of the 

 eyes at 10 inches, viz. 14 J°. This yields the perfect ortho- stereo- 

 scopic image. Hitherto there has been no standard to Avhich a 

 stereoscopic image could be compared to determine if the relief 

 in the image was too high or too low. In this instrument the 

 full apertures of both objectives are clear, and the illumination 

 in the tubes is the same. The Wenham is so well known that a 

 description is unnecessary. 



