902 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the tubular diapbragm-liolder also turning in the same way. The 

 arm attached to the polarizer serves to rotate it. 



Bausch and Lomb Optical Company's Fitting for Neutral Tint 

 Camera Lucida. — Fig. 163 shows the fitting adopted by the Bausch and 

 Lomb Optical Co. It is made of vulcanite, and the half ring to which 



Fig. 1G3. 



the frame holding the neutral tint glass is fixed fits on the cap of the 

 eye-piece. Tlie vulcanite is sufficiently elastic to obtain a good grip 

 of the eye-piece. 



Testing the Binocular Arrangement.* — Mr. J. Swift gives the 

 following directions for testing the binocular arrangement of a 

 Microscope. 



It is of the first importance that the reflecting surfaces of the 

 Wenham prism should be absolutely flat ; as the rays passing through 

 it are twice reflected before they emerge, the slightest error in the 

 surfaces will serioiisly impair the definition. For testing the quality 

 of the prism the tongue of the blow-fly may be viewed with a 1 in. 

 objective, and should be equally well defined in both fields. In this 

 testing the same eye should be used in viewing each image separately. 

 'I'he image in both fields should focus clear and sharp at the same 

 time, that is to say, after adjusting the focus in the vertical tube, the 

 other tube should not require the focus to be readjusted to make the 

 image as distinct as in the former ; this point should be tested with 



♦ 'The Microscope and Accessory Apparatus,' 1883, pp. 27-9. 



