336 



KNOWLEDGE & SCIENTIFIC NEWS. 



[January, igo6. 



Conducted by F. Shillington Scales, f.r.m.s. 

 Elementary Photo-micrography. 



{Continued from page 30S.) 

 Till-: room should now be darkened and a piece of white 

 paper held in the beam of light coming' from the bull's- 

 eye. By moving this backwards and forwards an ap- 

 proximate position can be found where the light comes 

 to a focus, and by slightly moving the Ijull's-eye it.self 

 this focus will be found to lengthen and shorten in- 

 versely as the corresponding conjugate focus from the 

 lamp-flame lengthens and shortens. When the bull's- 

 eye is adjusted to give parallel light the disc of light 

 upon the paper should be of the same size as the bull's- 

 eye, and should remain of the same size, neither more 

 nor less, whether the paper be brought towards the 

 illuminant or receded, and when looked through 

 directly, the bull's-eye should be full of light at all 

 distances. Unfortunalelv, the ordinary buirs-<'ye has 

 so many aberrations inherent to its simple form of 

 construction that only approximately parallel light and 

 only approximately focussed light can be obtained by 

 its means. The ordinary so-called " aplanatic " bull's- 

 eyes are only a degree better, and it is here that the 

 advantage of a really well-corrected condenser such as 

 that of Mr. Conrady (see " Knowledge " for June, 

 1905, page 138) becomes evident. A word may be 

 said concerning the large condensers, six inches or 

 so ill diameter, found on some Continental photo-micro- 

 graphic stands. Thev, of course, take in a large 

 amount of light, but they take in more, as Mr. Con- 

 rady says, than the objective can utilise, and, in addi- 

 tion, they generally consist merely of a couple of simple 

 uncorrected plano-convex lenses. The second method 

 of adjusting the condenser is to throw parallel or ap- 

 proximately parallel light upon the sub-stage condenser 

 direct, and with an ordinary bull's-eye this gives as 

 good or even better results than the method of focussing 

 10 inches behind the condenser just mentioned. Of 

 course, were the light really parallel, the sub-stage 

 condenser would bring it to a focus upon the object 

 once more, but this does not happen in practice. The 

 third method is to project the light into the plane of 

 the objective itself, and this is generally done with low 

 powers, especially those planar lenses of three inches 

 or more focus, which are used for low power work. 

 By this means the whole field can be uniformly 

 illuminated. 



But we now come to the most important adjustment 

 of all, namely, the due centring of all the optical ap- 

 pliances mentioned, and it is here that the worker will 

 feel the full advantage of those means of vertical and 

 horizontal adjustment for each piece of apparatus men- 

 tioned previously. First set up the microscope hori- 

 zontally so that the eye-piece end is connected with the 

 camera, and make the light-tight connection. Place 

 the illuminant a foot or more beyond the sub-stao-e so 

 as to shine through the tube. Then screw in a low 

 power objective and examine the disc of light upon the 

 ground-glass screen of the camera. 

 (To be coniimied.) 



Royal Microscopical Society. 



November 15, at 20, Hanover Square, G. C. Karop, 

 Esq., IVF.R.C.S., vice-president in the chair. The 

 Curator explained the Lucernal and Solar microscopes 

 by Adams, presented to the Society that evening by 

 Mr. Wynne H. Baxter. They were described by the 

 maker in the " Essays on the Microscope," published by 

 him in 17S7. Dr. Ilebb exhibited a magnifier made by 

 Messrs. Tavlor, Taylor and Hobson, of Berners .Street, 

 and Leicester. It was intended for focussing in photo- 

 micrography, being placed against the ground-glass 

 screen, and was provided with an adjustable draw-tube 

 and a screw ring to clamp the same. Dr. Hebb also 

 exhibited a turn-table, the joint invention of Mr. A. 

 Flatters and Mr. Wm. Bradley. It was driven by 

 clock-work and designed for turning oval cells and 

 ringing oval mounts from any size up to 3 by ij 

 inches. By means of this turn-table, it was also 

 possible to run a ring around a needle point, to turn 

 circles, or to strike a straight line. An additional 

 chuck, by means of which square covers also could be 

 sealed, was not satisfactory in performance. The 

 Chairman, whilst remarking on the ingenuity of the 

 instrument, observed that it was doubtful if anyone 

 present at the meeting would have occasion to mount 

 objects in such numbers as to need so elaborate an ap- 

 paratus. Mr. R. W. Paul sent for exhibition a Nernst 

 lamp, for use with the microscope and for enlarging 

 photographs, but was unfortunately unable to be pre- 

 sent to explain its advantages. Mr. F. W. Watson- 

 Baker exhibited a .series of dissections of the Tsetse 

 fly and its Trypano,somes, from South .'Xfrica, also a 

 specimen of the larva of Ochromyia, together with the 

 perfect insect. The larva also comes from .South 

 Africa and lives in the sandy earth, attaching itself 

 to the flesh of natives and causing troublesome wounds. 

 There was also a specimen of the ova of Schistosoma 

 Sinensis, found in the body of a Chinaman, who died at 

 Singapore. 



The Quekett Microscopical Club. 



The 425th ordinary meeting of the Quekett Micro- 

 scopical Club was held on November 17, at 20, 

 Hanover Square, W'., the Rt. Hon. Sir Ford North, 

 F.R..S., a \'ice-President, in the Chair. There was, as 

 usual, a crowded meeting. 



Mr. H. Taverner, F.R.M.S., described a method of 

 finding the depth of cells sunk in glass slips, by means 

 of an engineer's internal depth gauge, reading with a 

 vernier to within r,V of a millimetre. He had found 

 this a very ready and accurate method of judging the 

 depth of cell required for objects to be mounted with- 

 out pressure, whose thickness was already known. 



It had been announced that the President, Dr. E. J. 

 Spitta, F.R..V.S., F.R.M.S., would read a paper "On 

 some Experiments relating to the Insect's Compound 

 Eye," but owing to his unavoidable absence through 

 illness, a lecture by Mr. Frank P. Smith on " Spider 

 Eyes," was substituted, .'\fter describing the diflfer- 

 enoes between the two distinct types of simple eye 

 which had been found in spiders, and which were dis- 

 tinguished as "nocturnal" and "diurnal" eyes, the 

 lecturer proceeded to describe the arrangement of the 

 eyes in the various families, \vhich was found to be 

 more or less connected with the life habits of the ani- 

 mal. He then described some of the abnormal types 

 which had been observed and speculated as to their 

 probable origin and meaning. A discussion followed 

 in which several members took part. 



Microscopists desirous of joining the Club at the 

 commencement of 1906, should communicate with the 

 Hon. Sec, Mr. A. Earhnd, 61, Denmark Street, Watford. 



