28o 



KNOWLEDGE & SCIENTIFIC NEWS. 



November, 1905. 



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

 Elementary Photo-micrography. 



] H.WK bcx-n frequently ;i>ke(l to _<;i\e some information 

 on photo-micrography which would assist absolute be- 

 ginners. In endeavouring to act upon the suggestion 

 it must be understood that these notes make no at- 

 tempt to instruct those who are already more or less 

 expert; absolute ignorance of the whole matter is 

 assumed as a basis. For this reason, also, my remarks 

 will deal with the mere elements of the subject only. 



The first question that is invariably asked is whether 

 a regular photo-micrographic camera is necessary. I 

 am afraid that the answer must he in the aflirmative. 

 The main reason for this is that absolute rigidity and 

 absence of movement is a sine qua non. An ordinary 

 photographic camera could doubtless be fitted to aii 

 efficient baseboard by anyone with a mechanical turn, 

 or who is used to carpentry, but the adjustments would 

 be less satisfactory than in a camera made and designed 

 specially for the purpose, whilst the cost of making 

 such a baseboard and adding the necessarv fittings and 

 connections would go some way towards the cost of a 

 proper camera. A further reason is that the ordinary 

 camera has insufficient bellows extension. A modern 

 photo-micrographic camera extends to at least thirty 

 inches, and often to very much more. Of course, I 

 have seen photographs taken with an ordinary camera, 

 supported at the necessary height by books of the 

 requisite thickness, but though they seemed to plea.se 

 their authors I am afraid they would not bear ordinary 

 criticism. 



The next question is as to the respective advantages 

 of a horizontal and a vertical camera. Dr. Henri Van 

 Heurck, the well-known diatomist, has done nearly all 

 his work with a vertical camera, and there is much to 

 be said in its favour. It is convenient to use; the 

 micro.scopc is in the upright position to which the 

 observer is accustomed, and the adjustments of the 

 microscope are thus more familiar to him, especially 

 because he continues to use the mirror to reflect the 

 light; it is easy to draw the camera-bellows up out of the 

 wav, to make most of the adjustments in the ordinary 

 manner, and then to make the final connections, 

 whilst if the camera is of the box type with a large 

 door through which the head can be put to look down 

 the microscope tube the matter is simpler still. More- 

 over, there are certain cases, such as those in which 

 the object is but temporarily mounted, sav, in water or 

 otherwi.se, in which the microscope must be kept up- 

 right. But I think there can Ix; no doubt that the 

 horizontal camera is mf)re satisfactory for all-round 

 work, and, as a result, it is generally used and pre- 

 ferred. Its .solid base gives complete rigidity, with, at 

 the same time, every facility for long extension, and it 

 lends itself in particular to the adjustment of illuminant 

 and microscope with their intervening accessories, and 

 more especially to the newer arrangement of optical 

 bench, which has done .so much to simplify and co- 

 ordinate the necessary optical adjustments. 



I do not propose to speak here of the more elaborate 

 forms of photo-micrographic camera. I am writing 

 for beginners, and, therefore, the simplest camera is 

 the best for them. It must have a solid and steady 

 base, and nicely turned legs must be conspicuous by 

 (heir absence. The part of the base which supports 

 the microscope must be long enough to hold not only 

 the microscope, but the lamp or other illuminant, and 

 there must be room between the two for condenser, 

 cooling-trough, and stand for coloured screens. All 

 these should Ix; arranged on stands running be- 

 tween parallel guides so as to maintain their align- 

 ment with the optic axis of the microscope, whether 

 they are brought forward or pushed back; the stands 

 should be square and not round for the same reason, 

 and there must Ijc means by adjustable bars and by 

 centring screws or otherwise of making the vertical 

 and horizontal adjustments, which will be found to be 

 necessary for each piece of apparatus, and which will 

 prove an important factor in the results. The advan- 

 tage of the optical bench is now c\ident. In its 

 simplest form this is merely a heavy triangular iron 

 bar, carefully planed, screwed to the baseboard of the 

 camera, and carrying the light and optical accessories 

 on saddle-shaped Ijases on its edge. As I have already 

 said, this simplifies matters marvellously, cncc the 

 primary adjiisimatts arc made, but a couple of parallel 

 wooden guides make a quite efficient if less convenient 

 substitute. 



The camera itself will be raised a few inches higher 

 than the rest of the baseboard, so as to bring its centre 

 level with the centre of the microscope tube. It should 

 extend to at least thirty inches, w-hilst many extend to 

 sixty inches. The fittings of the camera will be de- 

 scribed in due course; here I may just say that the 

 light-tight joint may be nothing more elaborate than a 

 loose sleeve of black velvet attached to the camera 

 front and slipped over the microscope tube and held 

 there in place by a rubber band or ring of elastic. A 

 shutter must, of course, be provided. 



The camera and baseboard must all be made of care- 

 fullv-seasoncd mahogany, and the camera must run 

 smoothly and truely in its slides. The dark-slides, &c., 

 should be constructed to take half-plate slides, and 

 should have carriers to take quarter-plate slides as well. 

 I need scarcely say that it is absolutely essential that 

 the plates and the focussing screens must all lie at 

 exactly the same distance from the microscope. 



A camera of this sort can lie obtained from all the 

 leading opticians from jQ^ upwards, ruid I)oth R. iV J. 

 Heck, and W. Watson and .Sons make, in addition, the 

 optical benches to which I have referred. 



Let us now deal with the illuminant. Lamp-light — 

 the light of an ordinary half-inch parairin microscope 

 lamp — is quite satisfactory for all but the most critical 

 high-power work, but, of course, it needs :i relatively 

 long exposure. An inch lamp is better. The incan- 

 descent burner is not satisfactory — it gives a good 

 light, but it is spread over too large a surface, and if it 

 is focussed it gives an image of the texture of the 

 mantle. Acetylene is really excellent, the light is 

 good, it is small, and it has high actinic properties. 

 The incandescent electric light is unsatisfactory, be- 

 cause the filament is too obtrusive; the electric arc- 

 lamp is best of all, but, of course, can be indulged in by 

 few who have not the rim of a laboratory, and so for 

 all-round work the oxy-hydrogen jet is th(! best for 

 private workers. It is strong enough, and has sufficient 

 actinic value to make the exposure as short as one need 

 rca.sonably wish it to be. 



t To he continued, j 



