63 



Note ox a New Arrangement for viewing Diffraction 



Spectra. 



By J. Eheinberg, F.E.M.S. 



[Read Becemher 2\st, 1900.) 



It is a matter of common knowledge that the diffraction spectra,, 

 which an object under the microscope gives rise to, may be 

 observed by removing the eyepiece and looking down the tube. 



A 



B 



a. Diffraction Spectra Ocular, which is arranged 



to fit on to the top of 

 B, the usual eyepiece. 

 The sliding collar 8 allows of adjustment to any power eyepiece. 



But unless the eye is kept perfectly steady, which is difficult, they 

 shift and change about. For this reason Dr. Johnstone Stoney, 

 I believe, recommended looking at them through a pinhole near the 

 eyepiece, a method which I followed for some time. This, though 

 it does away with the shifting, reduces the light very much. It 

 is also possible to view the spectra by screwing an objective into 

 the lower end of the sliding draw-tube, with eyepiece in position 



