369 



BINOCULAR MICROSCOPES. 



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

 (Bead. May 2tth, 1914.) 



Fig. 5. 



In recent years several binoculars have been introduced ; none 

 of them, however, can be called new. The first, the Greenough, 

 by Zeiss * in 1897 was a twin microscope, a form of binocular 

 invented by Pere Cherubin d'Orleans nearly three hundred years 

 ago. The second, by F. E. Ives in 1902,f is very similar to one 

 designed by Wenham in 1866 as a counterblast to Powell's 

 high -power binocular in which the whole beam is sent into 

 each eye. % The third is a modification of the second by Messrs. 

 Leitz, and the fourth, by Messrs. Beck, is very similar to that 

 of Ives. 



Before proceeding, let us enumerate the points gained by 

 binocular vision. They are four in number and were stated 

 by me in the English Mechanic || as follows : 



1. Stereoscopism, or the power of appreciating solidity. 



2. Increase of apparent magnifying power. 



3. Increase of illumination. 



4. Increase of colour perception. 



The first binocular we have to deal with, viz. the Greenough 

 twin microscope, became a practical form owing to the re- 

 introduction of the Porro prism by C. D. Ahrens in 1888. 

 Obviously, it can only be used with very low powers, but never- 

 theless I have had no reason to alter the favourable opinion 

 I expressed for this form of binocular when it was first ex- 

 hibited by Messrs. Zeiss. In this instrument all the above 



* Journ. B.M.S., 1897, pp. 599-600. 

 t Ibid., 1903, p. 85, Fig. 3. 



X I am indebted to Mr. Rousselet for kindly bringing the Ives binocular 

 to my notice. 



Journ. B.M.S., 1914, p. 5. 

 || 1911, Vol. 94, No. 2432. 



