NEW HUYGHENIAN EYE-PIECE 



377 



objective can stand, and as a rule even the centre of the field will 

 not bear comparison in sharpness with the Huygheniaii form. 



Mr. ISTelson has recently computed and had made a Huygheniaii 

 eye-piece on a Avholly new formula l which has the field reduced by 

 about 7 inches, yet we can testify that in use it gives exceedingly 

 sharp images, and what surprises the accustomed worker is that it 

 acts admirably in the place of 'compensated' eye-pieces, giving 

 results that often not only equal but surpass these. 



The power of this eye-piece is 12 ; equivalent focus, - 8, corrected 

 for the English tube (p = 9'5). 



Fig. 324 is enlarged twice. 



FIG. 324. Nelson's new formula Huyghenian eye-piece. 



Data: Glass, borosilicate crown, ^=1*51, v=64*0, Jena cata- 

 logue Ko. 5. 



Field-lens, biconvex r= + '94) -,. KK 



s= _ 2 . 9 4j diameter '55. 



Eye-lens, biconvex r'=-f- '34) -,. 



g/ __ 1 .Q 1 f diameter '30. 



Distance of eye-lens from field-lens, measured from their sur- 

 faces, -97. 



Distance of diaphragm from surface of field lens, '48. 



Diameter of hole in diaphragm, *26. 



Power, 12 ; equivalent focus, '53, corrected for the Continental 

 tube (p=6-3). 



Data : Glass, same as before. 



Field-lens, biconvex ^= + ^65) diameter . g5 



Eye-lens, biconvex /=+ -22 J diameter . 20 . 



Distance of eye-lens from field-lens, measured from their sur- 

 faces, -66. 



Distance of diaphragm from surface of field-lens, '34. 



Diameter of hole in diaphragm, '16. 



These eye-pieces should enter the tube of the microscope as far 

 as their diaphragms. 



Positive Eye-pieces. In the early compound microscopes the 



1 J.B.M.S. 1900, p. 165. 



