PBOCEEDINGS. OP THE SOCIETY. 939 



Mr. Watson's Nose-piece Adapter, and that of Dr. Matthews 

 (supra, pp. 903-4), were exhibited by Mr. Crisp. 



Dr. Matthews, in reply to a question as to the firmness with 

 which his adapter would hold an objective, said that as a proof of 

 how firmly this kind of connection would grip, he might say that a 

 1-inch bolt could be screwed in a lathe at one operation in a chuck 

 which was only fitted to the head-stock by a coned joint. 



Mr. Ingpen thought that in the case of the lathe-chuck the screw 

 pressed strongly against it during the operation, and that this pressure 

 of course increased the cohesion of the surfaces, but in the case of an 

 objective there would not only be no such pressure, but the weight 

 would act the other way. 



Dr. Anthony inquired if any provision was made as regarded the 

 centering of the objective, supposing that it was interfered with by 

 this mode of connection. 



Dr. Matthews said that all objectives were open to the difficulty 

 of centering, because each had its own centre, and no two of them 

 were alike. To get accuracy they must be fitted to the instrument on 

 which they were to be used. Those which were coned were no worse 

 in this respect than others, possibly they were better. 



Professor Abbe's Analyser was explained by Mr. J. Mayall, jun. 

 by means of a black-board diagram. 



Mr. J. Mayall, jun., exhibited and described a pocket-lens on a 

 new formula by Dr. Schroder. 



Mr. Ingpen asked if the lens was considered to be superior to 

 those of Steinheil. 



Mr. Mayall said he had recently the opportunity of comparing 

 the two, and thought the new one was greatly superior, both as 

 regarded length of working distance and more perfect achromatism. 

 It was so well made that he found it worked well wlien used as an 

 eye-piece. 



Mr. C. Beck remarked that the working distance of the new lens 

 was nearly an inch. 



Mr. Crisp read a paper " On Optical Tube-length, an Unconsidered 

 Element in the Theory of the Microscope" (supra, p. 816). 



Dr. Anthony said that the important point to ascertain in future 

 was the value of A, or the " optical tube-length," and he thought this 

 was a matter which might be easily got at. 



The President said it followed from the paper that in consequence 

 of the variation in the optical tube-length they could not formulate 

 any correct table of focal lengths. 



Professor Ahbe's paper " On the Kelation of Aperture to Power," 

 Part III., was read by Mr. Crisp (supra, p. 790). 



Mr. Mayall wished to call attention to one or two practical points 

 which had not been touched upon. With regard to the statement that 



3 R 'J 



