ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 255 



direction. For example, in observations upon the spectrum, or upon 

 interference bands, there is often no need to magnify much, or perhaps 

 at all, in the direction parallel to the lines or bands. If, nevertheless, 

 we magnify equally in both directions, there may be an unnecessary and 

 often very serious loss of light. The author has found the use of a 

 cylindrical lens (e.g., a glass rod, 4 mm. in diameter), give a very high 

 magnification in one direction, and it appeared that the combination of 

 such an eye-lens with a sloped object-lens constituted a very satisfactory 

 solution of the problem. After the reading of the paper before the 

 Royal Society, the author found that use of cylindrical lenses had been 

 previously made by Rudolf, Lippich, and S. P. Thompson, though with 

 differences in detail. 



c6) Miscellaneous. 



Quekett Microscopical Club. — The 454th Ordinary Meeting, which 

 was also the 43rd Annual General Meeting, was held at 20, Hanover 

 Square, W. s on Friday, February 5, 1909, the Right Hon. Sir Ford 

 North, F.R.S., Alce-President, in the chair. Mr. F. W. Watson Baker, 

 F.R.M.S., for Messrs. W. Watson and Sons, Ltd., gave a demonstration 

 on " The Making of a Microscope Objective." The chief exhibits were — 

 Examples of optical, flint- and crown-glass, with pieces " slit " ready for 

 working. An optical-worker's lathe, at which the preliminary stages in 

 the production of a lens were carried out. At another bench the final 

 figuring and polishing of a high-power " front " were shown, together 

 witli examples of " proof -plates," which take the place of the old- 

 fashioned templates. The 43rd Annual Report of the Committee was 

 read by the Hon. Sec, and the Hon. Treasurer presented his Report for 

 the year 1908. The officers elected for the year 1909 are the same as 

 for 1908. Dr. Duncan J. Read, M.B., CM., gave a lecture on "A 

 Method of Estimating the Exposure required in Photomicrography with 

 Axial Cone Illumination." With a given class of subject and with known 

 N.A. and magnification, the correct exposure is obtained experimentally. 

 A table is constructed for this N.A., calculated for other magnifications 

 in the usual method. When employing other N.A. it is necessary to 

 measure this immediately before making the exposure, and to apply a 

 correction from a second table. The N.A. may be obtained as follows : 

 Measure the diameter of the Ramsden disk of the ocular. Multiply 

 half this diameter by the magnifying power of the ocular, and divide 

 by the focal length of the objective. This gives the required N.A. 



The 455th Ordinary Meeting was held on March 5, Dr. E. J. Spitta, 

 F.R.A.S., F.R.M.S., Vice-President, in the chair. A paper on " The 

 Structure of the Eye Surface, and the Sexual Differences of the Eyes in 

 Diptera," communicated by Mr. W. Wesche, F.R.M.S., was read by 

 Mr. F. J. Perkes. Mr. T. B. Rosseter, F.R.M.S., gave an account of 

 some recent work on the genus Hymenolepis (avian tapeworms), and 

 described a new species, Hymenolepis accicula-sinuata sp. n., taken 

 from Anas boschas for a. This will be fully dgcribed and figured in the 

 next issue of the Journal of the Quekett Microscopical Club. 



