JOUENAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY 



OCTOBER 1900. 



TRANSACTIONS OF THE SOCIETY. 



VIII. — A New Projection Eye-piece and an Improved Polarising 



Eye-piece. 



By E. B. Stringer, B.A. 



(Bead 20th June, 1900.) 



I have for some time past used for projection a positive eye-piece 

 consisting of a single combination of Steinheil's construction. Its 

 advantages for the purpose are, I believe, not known. It is indeed 

 mentioned in Dr. Dallinger's edition of Carpenter as making a good 

 eye-piece for visual work ; but the reason it has been so little used for 

 this purpose (if used at all) is probably because the field it gives is so 

 small, and because only the lowest powers work really well ; nothing 

 above x 6 yielding perfect results. 



But these, whilst being drawbacks to its use for visual work, are 

 by no means so for projection. A projection eye-piece is always of 

 low power, and smallness of field is desirable, or even necessary. 

 Moreover, owing to its having only half the number of reflecting 

 surfaces, this lens yields an image of greater brilliancy than the 

 Huyghenian combination ; and the greater flatness of field and 

 absolute freedom from distortion in the projected image also give it 

 a decided advantage. 



It may of course be easily made either over- or under-corrected for 

 use either with apochromatic or achromatic objectives ; thus affording 

 if necessary a projection eye-piece for use with the latter; a thing 

 which has not hitherto been available. 



I have devised a mount for this lens for photographic purposes in 

 which the connecting flange is attached to the eye-piece itself, and 

 is graduated, and when made to rotate, causes the lens to travel back- 

 wards or forwards by means of a spiral slot, so that the diaphragm 

 may be focused on the screen. The graduations on the flange (which 

 are read off against the stationary pointer attached to the body of the 

 eye-piece) are made empirically, the numbers representing the camera 

 length in inches, so that the eye-piece may be instantly put into 

 adjustment without the troublesome trials previously necessary. 



Oct. 17th, 1900 2 o 



