KNOWLEDGE & SCIENTIFIC NEWS. 



[Jan., 1905. 



Conducted hi/ F. Shii.lington Scales, f.r.m s. 



Royal Microscopical Society. 



XovEMBER i6th, Rt. Hon. Sir Ford North, F.R.S., in 

 the chair. Mr. Rousselet described two old micro- 

 scopes which had been presented to the Society by 

 Mr. C. L. Curties. The first was a copy by Doilond 

 of Cuff's " New Constructed Double Microscope," 

 designed by Cuff in 1744, in which the body was moved 

 instead of the stage, the latter being customary in 

 microscopes of later date. The second microscope 

 was a copy of " Jones' most improved compound 

 microscope," made and modified by Banks, between 

 i8ii and 1820, though the invention of this type dates 

 from 1798. Mr. Hugh C. Ross, R.N'., exhibited and 

 described a new electric warm stage of his invention. 

 It consisted of a flat plate or box of ebonite about 

 3 inches long, li inches wide, and f inch thick. A 

 coil of wire offering a standard resistance was pressed 

 into the ebonite box and covered in w-ith a sheet of 

 mica. The ebonite box rested on the slide, mica side 

 downwards, and a gap i inch square was left in the 

 centre of the stage so as not to interfere with the 

 examination of the object. A Nernst lamp served 

 both as iliuminant and regulator of the current to the 

 warm stage. It was claimed that this warm stage, 

 being used above the slide, did not interfere with the 

 focus, could be used with the highest powers, allowed 

 the use of a condenser, did not interfere with the move- 

 ment of the mechanical stage, and was self-acting. 

 Mr. C. L. Curties exhibited new designs of Nernst 

 lamps suitable for use with the microscope for currents 

 of 100 and 200 volts respectively, and fitted with 

 ground or blue glass fronts. Mr. Conrady read a 

 paper on " Theories of Microscopic Vision. A vindica- 

 tion of the .Abbe Theory," which contained some new 

 views on the suhjfrt. 



The Quekett Microscopical Club. 



The 417th Ordinary Meeting of the Quekett Micro- 

 scopical Club was held on November i8th at 20, Han- 

 over Square, W., the President, Dr. K. J. Spitta, 

 V.P.R.A.S., in the chair. Mr. A. E. Smith exhibited 

 a number of large transparencies, prepared from his 

 own photo-micrographs. Notes by Mr. A. E. Merlin, 

 F.R.M..S., " On a suggested modification of Rousse- 

 let 's Live Box " and " A supplementary note on the 

 foot of the House Fly " were, in the absence of the 

 author, read by the Hon. Secretary. In the first note 

 Mr. Merlin, after paying tribute to the manifold ad- 

 vantages of the Rousselet Live Box, alluded to the 

 fact that the comparatively rapid evaporation of the 

 water film prevented any prolonged observation of 

 minute organisms such as monads, &'C., under high 

 powers. If, however, the cover-glass is cemented to 

 the flange instead of being screwed in, and if a rubber 

 band is slipped round the junction of the box and the 

 carrier, a practically airtight joint is formed, and 

 evaporation proceeds so slowly that he had been able 

 to keep an object under observation for several days. 



Mr. Merlin's second note was a continuation of two 

 previous papers on the same subject read before the 

 club in 1S95 and 1S97. He now reported that he had 

 succeeded in detecting a small knob or protuberance on 

 the side of the sickle-shaped terminal appendages of 

 the hairs of the pulvillus, which knob, in his opinion, 

 marked the position of the aperture through which the 

 viscid secretion was poured out. He h.id not, how- 

 ever, been able as yet to detect the aperture with the 

 highest optical power at his disposal, viz., i" apochro- 

 mat by Zeiss of N.A. 1.427 and a 40 compensating 

 ocular. Even with this magnification the image of 

 the sickle filament was sharp and clear. 



Mr. A. E. Conrady, F.R.A.S., F.R.M.S., then gave 

 a rtsume of his important paper " Theories of Micro- 

 scopical \'ision — a Vindication of the .Abbe Theory," 

 which had laeen read before the Royal Microscopical 

 Society on the previous Wednesday. 



Micro-photographs. 



The term micro-photograph is used in England to 

 distinguish minute photographic reductions of larger 

 objects in contradistinction to photographs of enlarge- 

 ments of microscopic objects which have been magnified 

 by means of the microscope, and which arc known as 

 photo-micrographs. In the " Photographic Reference 

 Hook " for 1904 an account is given of the method of 

 preparing such micro-photographs, of which the follow- 

 ing brief resume may be of interest. They require 

 considerable patience and skill, as the image is so 

 minute that the operations of development, &-c., must 

 be carried out in the field of a magnifier or small micro- 

 scope. Most of these photographs are made abroad, 

 and the collodion process (wet plate) is used, or 

 collodio-albumen may be employed. The collodion 

 used for making the plates must be structureless or the 

 magnified images will have a reticulated appearance. 

 Pyrogallic acid is preferable to iron sulphate for de- 

 velopment, as it gives a much finer deposit. The 

 process consists in making a positive by copying an 

 illuminated negative, using a one-inch microscopical 

 objective for this purpose. Mr. Hislop has devised a 

 suitable apparatus, which is described in Mr. .Sutton's 

 " Dictionary of Photography." It consists of a rigid 

 mahogany board about six inches wide and three feet 

 six inches long. At one end two uprights are fixed, 

 between which a miniature camera, fitted with the 

 microscopical objective, can be moved up and down so 

 as to allow it to be placed opposite the negative to be 

 copied. A brass tube projects from the camera to- 

 wards the negative, to carry the objective, and is fitted 

 with stops of different sizes. The exact focus must be 

 ascertained carefully by means of a strong magnifying 

 glass. The negative is placed in a frame at the re- 

 quired distance on the long mahogany board. The 

 illumination may be natural or artificial, but must, of 

 course, pass through the negative, whilst the variations 

 of light, negative, and pk.te, render it impossible to 

 give any idea of exposure. It will generally be found 

 that the visual and actinic foci do not coincide, and 

 this must be determined by experiment and allowed for, 

 so that a fine adjustment becomes necessary. After 

 exposure the little plate is placed under a low power 

 microscope, in yellow light, and a few drops of de- 

 veloper poured over it, development being carefully 

 watched through the microscope, remembering that a 

 transparency is required, and, therefore, greater density 

 than otherwise should be obtained. After fixing and 

 drying, and before mounting, the tiny plates should be 



