3o8 



KNOWLEDGE & SCIENTIFIC NEWS. 



[December, 1905 



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

 Elementary Photo-micrography. 



{Coutiiiucil from /rtg'<" 2S0.) 

 U.VDER any circumstances the lamp or other source of 

 illumination must be provided with some means of ad- 

 justing it both vertically and laterally. This is nearly 

 always provided with the oxy-hydrogen jet, and the 

 ordinary microscope lamps are generally supplied with 

 an upright rod upon which they move vertically. The 

 horizontal adjustments are easily obtained by arranging 

 a wooden stand to run lengthwise in the parallel guides 

 of the baseboard, and another stand above this running 

 in parallel guides, who.se motion is across and at right 

 angles to the lower stand. The two can be clamped 

 together with a thumb-screw. Such an arrangement 

 could easily be made at home. 



It will be found a great convenience if a similar stand 

 be made for the microscope, but the more general 

 method is to arrange a clamp of some sort and shoulders 

 against which the foot may come so that once the 

 microscope has been definitely adjusted in its proper 

 position and the shoulders fitted accordingly it may be 

 an easy matter to replace the microscope at any time 

 and to clamp it securely, with the certaintv that it is 

 correctly placed. The Continental stand with its horse- 

 shoe base is so unsteady when in the horizontal position 

 that it absolutely needs some such clamping arrange- 

 ment, but the English tripod is nearly as steady in this 

 position as when upright, and in the case of one of my 

 own microscopes I have merely to drop the three feet 

 of the stand into three little metal rings screwed on to 

 the baseboard and which were carefully placed correctly 

 once for all. 



The loss of light in photo-micrography is so consider- 

 able that some means of strengthening the illumination 

 is necessary, and this is done by means of an auxiliary 

 condenser placed between the light and the sub-stage 

 condenser of the micro.scope. A further necessity for 

 such an auxiliary condenser is due to the importance in 

 photo-micrography of equally illuminating the whole 

 field of view. With ordinary visual microscopic work 

 this is not necessary, and the advanced microscopist 

 rigidly focu.ses his lamp flame with a view to getting 

 the lx;st image in the particular portion of the field 

 under examination, and cheerfully neglects the com- 

 paratively ill-illuminated portions of the field on each 

 side. But this is manifestly not admissible in a photo- 

 micrograph, and any alteration in the focus of the sub- 

 stage condenser to do away with this light streak would 

 not only depreciate the image, but cause a considerable 

 loss of light. So the auxiliary condenser is intcrpo.sed. 

 There are three ways in which this condenser can be 

 adjusted, and this is a point that is generally in- 

 sufficiently dealt with in books on the subject of photo- 

 micrography. To begin with, the auxiliary condenser 

 can be adjusted to give parallel light or converged light. 

 Of these, the second is the one usually u.sed, the bull's- 

 eye being so adjusted as to bring the light to a focus 10 

 inches or so away from the sub-stage condenser, which 



is then focussed on this point. A little experimenting 

 with the bull's-eiie in various positions will be found 

 very instructive and helpful. The plane side of the 

 bull's-eye should be turned towards the light and 

 brought comparatively close to it, as in this position 

 the aberrations of the ordinary uncorrected nearly hemi- 

 spherical bull's-eye are least in evidence. 

 (7\> he contiiincd. ) 



Royal Microscopical Society. 



.\t a meeting licld on October iS at 20, Hano\er 

 Square, Dr. Dukiiilield H. Scott, F.R.S., President, 

 in the chair, an old Wilson screw-barrel simple micro- 

 scope, date about 1750, presented by Major Meade J. C. 

 Dennis, was described by the Secretary, who traced 

 the history of microscopes, focussing by means of a 

 screw cut on the body-tulae, from Campani in 1686, 

 Grindl in 1697, Bonnani in 1691, Hartsocker in 1694, 

 to Wilson in 1702, who was followed bv Culpepper 

 some time prior to 1738, and Adams in 1746. Mr. V.. 

 .Moffat exhibited and described a simple portable 

 camera for use with the microscope. It consisted of a 

 vertical telescopic standard drawing out to 28 inches, 

 with .1 clamp at its lower end to secure it to the edge 

 of the table. At the upper end of the standard was 

 fixed a mahogany board, J inch thick x 4 ins. x 5 ins., 

 hinged at the pillar so as to close up, and having a 

 hole in the centre about 3 ins. in diameter. There were 

 two spring clips for .securing the dry-plate while 

 making the exposure, and guides for keeping it in 

 position horizontally. The back of the dry-plate was 

 covered by a piece of cardboard painted dead black, 

 the spring clip referred to pressing upon this card. 

 Depending from the board was a tapered bag of black 

 Italian cloth about 17 ins. long with a rubber ring at 

 the lower end to secure the covering to the eyc-picce of 

 the microscope. The apparatus can be closed up into 

 a space 5 ins. X 9 ins. x li ins., and will thus go into 

 a large pcx:ket or a knapsack. If made of aluminium 

 the weight should not exceed ij lbs. The designer 

 stated that this camera would work well up to 700 

 diameters, and could be made in brass for 21s., though 

 aluminium would cost more. The Secretary cxhil)ite{l 

 and described a hand microtome designed and used by 

 Mr. Flatters. It was made of brass .-md had .1 tube 

 3 ins. long and i in. inside diameter. The spindle had 

 a screw of 28 threads to the inch, and was actuated at 

 the lower end by three interchangeable notched discs, 

 engaging with a spring stop, the tension of which 

 could be adjusted. .Si'ctions could thus be cut varving 

 from TjTs'jyn to 1255 inch in thickness for each notch that 

 the disc was turned. The knife-plate was made of 

 hardened brass. The aperture on the upper side was 

 of somewhat smaller diameter than the rest of the 

 tube to prevent the specimen turning. Messrs. R. and 

 J. Beck exhibited the Aske Finlayson "Comparascopc" 

 (described in " Knowledge " for November last, page 

 281). A paper was read by Prof. Henry (J. Hanks, a 

 corresponding Fellow of the .Society, entitled " Notes 

 on .'\ragotilc, a Rare Californian Mineral," first d - 

 scribed by Mr. F. V.. Durand in a paper read before the 

 Californian Academy of .Sciences on April i, 1872. 

 The President called attention to an exhibition of a 

 number of slides froin the collection recently pr«'sented 

 to the .Society by Mr. W. M. Bale, of .Melbourne, in- 

 cluding some exrellcntiv moimterl orchid seeds. 



Quekett Microscopical Club. 



At the 424th ordinary meeting of the Quekett Micro- 

 scopical Club, which was held at 20, Hanover Square, 



