ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 549 



struction and advantages are not a little perplexing both theoretically 

 and practically, but we transcribe them as they are given : — 



" 1. A very large prism, with perfectly plane surfaces, cemented 

 upon a glass disk. 



2. As this combined prism and disk is fixed by the maker, it 

 remains in place regardless of the whim of or want of skill in the 

 observer. 



3. The mounting of this combination is a brass nose-piece, which 

 slides into the tube and is fastened by a new form of bayonet-cat oh, a 

 novel feature in itself. 



4. The monocular nose-piece is separate and is fastened in the 

 tube in the same manner. 



5. The effect with the prism in place is quite as good in this 

 instrument as it is in the old forms when the prism is withdrawn, as 

 it permits the passage of [more] light [than is] possible in objectives 

 with the Society screw. 



6. While a little more time is consumed in changing from mono- 

 cular to binocular and back again than is the case in the old form, 

 the loss is fully compensated for by the absolute accuracy of the new, 

 which cannot get out of place. 



7. As low powers only are used in binocular instruments, a given 

 objective may be kept in the binocular nose-piece and the higher 

 power in the monocular, an arrangement almost as convenient as in 

 the well-known double nose-piece. 



8. The bayonet-catch above mentioned may be applied, and 

 probably will be in the near future, to objectives as a substitute for 

 the Society screw. The fit is as good, and the time saved in changing 

 objectives great." 



The binocular is also thus referred to in the ' Amer. Mon. Micr. 

 Journ.,' iv. (1883) p. 97 :— 



" Mr. Edward Bausch has devised a modified form of the Wenham 

 binocular. . . Instead of mounting the prism in a metal frame which 

 can be moved in and out, as in the ordinary form of binocular, the 

 prism is cemented to a glass disk which is fixed in a special nose- 

 piece. The nose-piece can be readily attached to the Microscope by 

 a spring-catch. 



In this way the prism is always secured in exactly the right place, 

 and when a plain nose-piece is substituted, as when high-power objec- 

 tives are used, there is nothing in the tube to reduce the angular 

 aperture of the lens. The arrangement is less convenient than the 

 ordinary plan, but if the advantages claimed for it are found not to 

 be of sufficient practical importance to lead to its final adoption, there 

 is no reason why the prism should not be mounted in the old way. 

 We do not yet appreciate the advantages of the separate nose-pieces, 

 and we understand that the makers desire to have the verdict of 

 microscopists concerning this matter, before they adopt the plan. 



The prism ife a very large one, and as the face which receives the 

 rays is fully exposed it will transmit a larger angle of aperture than 

 the Wenham prism, which is much smaller. It is well known that 

 the mounting of the Wenham prism cuts down the angular aperture 



