Nov., 1904.J 



KNOWLEDGE & SCIENTIFIC NEWS. 



279 



some iiiL-chanical aid. I have found that the simplest, 

 and perhaps easiest, methcd is to carelnlly bore and 

 file out a sound cork, or portion of a cork, so as to fit 

 not too tightly over the end of the objective, leaving a 

 fairlv substantial margin to give comparative rigidity. 

 Through this margin^ is bored a small hole pointing 

 downwards and inwards towards the optical axis, and 

 holding a tine sable-brush. The marking liquid may 

 be Brunswick black, or asphalte thinned to a suitable 

 consistency with turpentine. It is then oiily necessary 

 to adjust the brush up or down in its obliquely-placcd 

 hole so as to give a ring of the requisite size, to rack 

 the objective down towards the cover-glass until the 

 brush is in contact with it, and to rotate the cork ring 

 which holds the brush so as to describe the necessary 

 circle. The rotation should be in the opposite direc- 

 tion to the hands of a clock so as to avoid unscrewing 

 the objective on the one hand, or unscrewing the front 

 lens on the other, and for the same reason this direction 

 of rotation should be adhered to in putting the cork on 

 to the objective or in taking it off. Too much black 

 must be avoided, and the brush must be very carefully 

 pointed, or the ring is not made neatly and satis- 

 factorily. .Another method is to fit a cork on to the 

 objective in the same way but to allow it to project 

 somewhat, and to press into it a small brass ring with 

 a carefully ground edge. This ring is painted with the 

 marking fluid and brought down gently upon the cover- 

 glass, but it is difficult to make neat rings by this 

 means, and to be of much use the brass ring and the 

 consequent hole in the end of the cork have to be much 

 smaller than the bore which takes the objective, so that 

 the cork is not easy to file out, and the projecting ring 

 interferes with the field of the objective with low 

 powers, and with the focussing with high ones. 



Gla.re when using a Vertical Illunninator 



Workers on metal specimens who use the vertical 

 illuminator are aware of the glare which is constantly 

 present in the field of view, and often to such ;in obtru- 

 sive extent as to seriously diminish sharpness of 

 definition and perception of detail. This is generally 

 due to reflections from the inside f)f the mount of the 

 objective. This glare may be greatly reduced — in fart, 

 for practical purposes, eliminated, by placing an Iris 

 diaphragm close to the source of light and reducing the 

 aperture through which the light passes, by means of 

 this diaphragm, to such a point as will remo\e the 

 objectionable glare. It will be found that this will not 

 affect the brilliance of the actual image, for only pre- 

 cisely the amount of light that can be usefully utilized, 

 no less and no more, will pass through the objective. 

 A similar arrangement in connection with ordinary 

 photo-micrography removes the glare which is so often 

 objected to, from the inside of the body of the micro- 

 scope. 



Notes and Queries. 



.1. M. [lunhar, Cast Griqualand. 



Several correspondents kindly answer my query last 

 month by recommendin.;,' Hassairs •' Adulterations Detected " 

 (Longmans, I057) as a book which deals with the microscopical 

 examination of adulterated foods. It contains over 200 micro- 

 scopical illus rations. I am also referred to Rattershall's" Food 

 Adulteratioi.,' price J5S., wliich has photo-micrographic plates. 

 This last is an .American publication, but may he had in 

 London at Spon's. 



J. CarriniSton, East London, S.A. 



I would recommend you to j^et Lewis Wright's " Popular 

 Handbook to the Microscope" (iSijp), published by the 

 Religious Tract Society at 2S. Od. This is quite elementary, 

 and contains chapters oil some common microscopical objects. 

 .Mso Cross and Cole's •' Modern Microscopy" (ujc);), published 

 by Baillicre, Tindall, and (.'ox, at 4s. This deals most clearly 

 with the microscope and its use on the one hand, and with 

 mounting methods on the otlu'r. If yon have any special 

 ditVuulty I shall be glad 1" help yon with it. 



J. P. Hodges, firanjietown, Yorks. 



'I1i(! Ksohition oi Ainl'hipUuni j-cUmida has long been a 

 f.ivouvite task with amateurs, but it is really not so dillicult as 

 it seems. The first retinisite is to have the diatoms mounted 

 in a medium of suitaljlc refractive index, such as realgar, 

 though monobromide of naphthalin will do. The objective 

 should have an aperture of about 1-25 or more, and if the con- 

 denser is also an innnersion one the result will be the more 

 satisfactory. Search the slide and pick out a good diatom — 

 thev vary more than would be imagined. Can-fully centre 

 the condenser with a low power by means of tlie iris dia- 

 phragm, then bring the lamp-flame into the centre of 

 the field, using the edge of the flame and keeping 

 the tail-rod central. Focus the flame sharply with the 

 condenser. Now change the objective to the .^jth, and 

 without altering mirror or lamp recentre the flame and 

 refocus it. The transverse striations should now be seen 

 pretty clearly, and will not be improved by closing the 

 diaphragm. But if not successful proceed as follows : See 

 that the lamp is exactly opposite the microscope, and the 

 mirror adjusted so that the lamp-flame lies vertically in the 

 centre of the field. Adjust the slide so that the diatom also 

 has its long axis vertically in the centre of the field. Make 

 all other adjustments as before, taking pains with the centring. 

 Now beneath the condenser put a stop which has one 

 slit in it reaching from the edge to the centre, and about 

 ^ inch wide, placing tlie stop so that the slit lies to the front of 

 the condenser. .\ "slight tilt of the mirror in its gymbals may 

 be necessary to bring the striations clearly into view, and 

 a little adjustment within narrow limits sometimi-s worlis 

 wonders, but the principle is to throw a narrow and very 

 oblique beam of light longitudinally down the diatom. Of 

 course the image does not represent the real structure of 

 the diatom, and that is a point which has been much dis- 

 cussed. The resolution of diatoms is certainly not a waste of 

 time ; I question if anything so soon teaches a microscopist 

 how to use his instrument to best advantage, or if any other 

 study has given as much impetus to the demand for better 

 objectives, better corrections, and better apertures, and so 

 helped to bring about the comparatively recent great advance 

 in this respect. 



Microscopical Material. 



Mr. .Mfrc'd Death, of F)Ury St. h;dmunds, has kindly sent 

 me for distribution a (piantity of ICchiims spines. The cutting 

 and rubbing them down for mounting is, as Mr. Death says, 

 somewhat tedious work, Init they make beautiful objects for 

 either directly transmitted light or annular illumination, 

 generally known as "dark-ground." Mr. Death gives the 

 following rhumc of his method of procedure: (i) Make 

 transverse section, as of any h.ird tissue. (2) Rub one 

 side quite smooth upon a hone, preferably VVater-of-Ayr 

 stone. (3) Fasten smooth side upon glass slip with Canada 

 balsam. (4) Grind section on glass upon hone until suniciently 

 thin. (3) Remove section from hone by warming over spirit 

 lamp. (Ol Fass through alcohol into clove oil and mount in 

 Canada balsam. I shall be pleased to send one or two of 

 these spicules to any reader who sends me a stamped 

 addressed envelope, together with the coupon appearing in 

 another part of this issue, and it will be a convenience to me 

 if applicants will enclose in the envelope a small piece of 

 tissue paper in which to fold the minute spicule. 



[Commtintcalivns and fm/iihies mi Miii'iKwopiuil matlcn iii-d invilcJ, 

 and ihuitld he addressed to F. Shillingtvn Scales, ••Jersey, "St. 

 Barnabas Huad, Cambridge.] 



