June, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



139 



in a Russian iron case. The usu il lar^^e condenser of 

 two simple plano-convex lenses is replaced by an achro- 

 matic and aplanatic doublet about 2 J ins. diameter, which 

 projects a sharp, enlarged, aerial image of the source of 

 light. The corrections of this condenser are of an un- 

 usually high order. Condensers of four inches or more 

 have generally been considered essential, but a little 

 consideration will show that no microscopical apparatus 

 can utilize a cone of light of so large an angular extent, 

 whilst the spherical aberration of all but the innermost 

 zone of such uncorrected condensers is so considerable as 

 to render the greater portion of these lenses quite useless 

 for practical purposes. Thus the small but really aplana- 

 tic condenser yields a brighter illumination than could 

 otherwise be utilized, because losses by absorption and 

 reflection are reduced to a minimum, whilst those due to 

 spherical aberration are entirely done away with. In 

 fact, the clear diameter even of this condenser is too 

 large for most microscopical purposes, and an iris dia- 

 phragm is therefore provided close to the lens so that its 

 aperture may be reduced to any desired extent. The 

 condenser is so adjusted as to project an aerial image of 

 the source of illumination from 10 to 15 ins. away from 

 the microscope stage — i.e., at a suitable distance from the 

 sub-stage condenser of the microscope. In the plane of 

 this aerial image is provided a second iris diaphragm, by 

 means of which the flame image can, if necessary, be re- 

 duced to such a size as will just cover the amount of 

 object that is to be photographed. This second iris dia- 

 phragm also materially assists in diminishing internal 

 reflections in the microscope tube. A thin auxiliary lens 

 is provided as an accessory which, when placed close to 

 the intermediate diaphragm, forms an image of the large 

 condenser on the iris of the second condenser, thus 

 collecting all the light passing through the latter, and 

 filling even large sub-stage condensers with light. For 

 low powers the large aplanatic condenser alone can be 

 adjusted so as to project an image of the source of light 

 on the diaphragm of the lens in use, thus evenly illumma- 

 ting objects two inches or more in diameter. The usual 

 cooling trough is provided. I have been using this 

 apparatus for some time and have found that the neces- 

 sary adjustments are very readily made by means of the 

 iris diaphragms, and that once made they require but 

 Ittle subsequent alteration; in fact, it is only a matter of a 

 fewminutestoremovethemicroscope from the table where 

 one is working and to place it m position for photography, 

 with the knowledge that very simple adjustments will 

 give perfect optical results. The condenser not only 

 gives unu ually perfect illumination, but very consider- 

 ably reduces the necessary exposure. I do not, of 

 course, mean to imply by this that successful photo- 

 micrography is merely a question of optical adjustment 

 and exposure. 



Notes and Queries. 



J. E. Blomficld [Scvcnoaks). — I am afraid you will not find 

 anyone who lays himself oat to supply the rarer fresh-water 

 algae. I have made inquiries here and cannot hear of any 

 such person. An advertisement might be of use. Do you 

 know Prof. G. S. West's " British Fresh-Water Alga; " ? — it 

 contains useful hints as to collecting. 



John Hume {Nc-u'casllc-on-Tync). — Soft sections want very 

 careful dehydrating and clearing. The alcohols must be care- 

 fully proportioned, as 30 per cent., 50 per cent., 75 per cent., 

 and 95 per cent., and the section should stay a good time in 

 each bath. It would be best to clear in xylol and mount 

 in xylol-balsam, and it would be advisable to have an inter- 

 mediate bath of hall xylol and half alcohol between the 95 



per cent, alcohol and the xylol. Perhaps also your sections 

 are too thick, in which case they do not get properly per- 

 meated with the media and shrinking at one stage or another 

 is very likely to happen. Benzine and benzole are different 

 names for the same substance. Sections preserved in alcohol 

 cannot be stained with carmine or haematoxylin made up as 

 watery stains — alcoholic solutions must be used. Probably 

 your trouble is due to your overlooking this fact. Eau dejavelle 

 is practically hypochlorite of potash, and in using it you 

 are putting back into the section the water which the alcohol 

 had removed, alcohol being essentially a dehydrating agent. 

 Sections stained with a watery solution of haematoxylin 

 should mount well in glycerine jelly if properly stained. After 

 staining, they should be washed in tap water, not distilled 

 water. This deepens and fixes the colour, owing to the calcium 

 salts it contains. 



jY. L. Gillespie (Fulham). — Slides for sending abroad are best 

 packed in the little wooden boxes which can be obtained from 

 the opticians, fitted with upright racks. They are very cheap. 

 Each slide should have its edges well packed into the rack with 

 cotton wool. A good way, however, is to fold a strip of paper 

 of suitable length into a strip one inch wide, so that it contains 

 several thicknesses of paper, and then fold two such strips in 

 and out between the ends of the slides, one strip at each end, in 

 in such a way that a double tongue of the strip lies between 

 the ends of each slide, projects inwards for about an inch (not 

 reaching the mount), and so separates it from those imme- 

 diately above and below. The nest of slides is then tied 

 tightly round with string and carefully packed in any haudy 

 box. Care must, of course, be taken that the last slide of 

 the nest has its mount turned in.vards for protection like the 

 others. 



/. Cooper (Wi'^an). — The best pocket lenses are those made 

 on the Steinheil principle. They are aplanatic — which means 

 flat in the field right up to the margin of the lens — and achro- 

 matic, or free from colour. They are of brilliant definition 

 and a great comfort to the eyes. Such lenses are known as 

 aplanatic pocket lenses, and are made by all the leading 

 microscope makers (see the advertisement columns of this 

 Journals and there is little to choose between them. They 

 cost from 12s. to 153. each, and the powers run 6, 10, 15, 

 and 20, or thereabouts. I think 5 is the handiest size, and 

 certainly it is the most comfortable to use ; the higher powers 

 are very tiring to the eyes. The lens should be mounted for 

 the pocket. 



/. Strachan (Ballyclare). — With reference to my recent 

 article on the Fibrous Constituents of Paper I must confess 

 that I have never found anj- quantitative method of esti- 

 mating the percentages of various fibres to be trustworthy, 

 except in a very rough and ready way. Your method of 

 counting the various fibres is probably the best and is accurate 

 within its limits, but is very laborious ; and I am afraid I 

 must ask you to forgive me if I am not able to check your 

 results as my time is very fully taken up with work of many 

 kinds. If you will be good enough to send on the samples 

 of chemical wood pulp and mechanical wood pulp, which 

 you kindly offer, I shall be glad to accept them on behalf of 

 my readers, and to distribute them to any who care to apply, 

 provided they will enclose a stamped addressed envelope for 

 the purpose. 



A. H. Glaister (Darlington). — Your method of marking the 

 actual magnification on the negative of a photo-micrograph 

 has been ofte.i used, but I am obliged to you for your com- 

 munication; and as some of my readers may not know of it, 

 I will give the method herewith as emanating from you. 

 Briefly, it consists in first taking a photo-micrograph and then, 

 without altering the adjustments of camera-length, tube- 

 length, eyepiece or objective in any way, of replacing the 

 dark-slide by ground-glass, and projecting thereon the lines of 

 an ordinary stage micrometer. The distance between the 

 lines is then marked on the edge of a slip of paper, and this is 

 used as a template, by which the marks can be scratched 

 across the negative at the side of the photograph. The 

 value of the lines is added, and the whole reproduces on the 

 positive as part of the photograph. 



[Communications and enquiries on Microscopical matters are invited, 

 and should be addressed to F. ShiUington Sc^ihs, "Jersey," 

 St Barnabas Road, Cambridge ] 



