392 



KNOWLEDGE & SCIENTIFIC NEWS 



[March, 1906. 



Conducted by F. Shili.ington Scales, p.. a., f.r.m.s. 

 Elementary Photo-micrography. 



[Cpntituicd from pag( 362.) 



The iitmosl crirp iiuisl he taken in ohservinq- whether 

 this disc of lig:ht is u-:illy iinifnirii; i| is somewhat decep- 

 tive, and a shght rc-adjiistmcnt may sometimes make 

 all the difference, hut if it be not uniform, the photo- 

 graph will show unequal illumination, that is, one side 

 will be rather darker than the other, which is not satis- 

 factory, though too often seen. The sub-stage con- 

 denser and even the auxiliary condenser mav need 

 sJight re-adjustment and re-focussing to obtain the best 

 results, but any great alteration will not be found satis- 

 factory. A little patient exjK'rimenting, however, will 

 be found to teach more than many pages of sugges- 

 tions. 



The advantage of the optical bench or of the parallel 

 slides is now evident, and if there is any change of ob- 

 jective a slight re-adjustment of the condenser is all 

 that is necessary. It saves much labour if everything 

 is lei I in place, except the microscope, and the position 

 ol thr laltiT is carefully marked, or stops made for its 

 stand, but if the auxiliary condenser and illuminant 

 must be removed, then some means should be .adopted 

 ot so arranging or marking them that they can be, 

 without (lifliculty, brought back exactlv to their previ- 

 ous position when required. 



So far, we have done all our focussing upon a piece 

 of ground glass, but this, however fine it may be, will 

 be found too coarse for the final focussing. We must, 

 therefore, have a further frame of plain glass, fitting 

 into the same slides, and once again I must insist on 

 the importance of having the inner surface of this in 

 exact correspondence with the sensitive film of the 

 photographic plate when in its dark slide and in posi- 

 tion. It is not a bad plan to fasten a thin circular 

 cover-glass with Crmada balsam, in the very centre of 

 the inner and rough side of the ground-glass screen. 

 This makes a little transparent disc for examining the 

 photograph, but it is scarcely big enough to be an 

 eflici^'nt substitute for the complete plain-glass screen. 

 In using the latter we have, of course, no surface to 

 form an image upon, and we therefore need a focussing 

 lens of some sort. This may be of the simplest form, 

 but its magnification should not be too high and yet its 

 " depth of focus " should not, for ma.nifest reasons, be 

 too great. A dissecting loop in a cardboard or wooden 

 ring will serve, or one of the ordinary tripod magnifiers, 

 but suil;ible lenses with a ring for adjustment, i.in be 

 bought for a few shillings at most opticians. An ink 

 mark is made on the inner surface of the plain glass 

 screen, the focussing lens is brought in contact with 

 the other or outer side, and then adjusted so as to 

 focus the ink-mark through the glass. Dr. Bousfield 

 recommends a double convex spectacle lens of about 

 eight inches focal length, w^hich may be mounted in a 

 cardboard or other tube of suitable length to focus such 

 an ink-mark. 



(To he conlinucd.) 



Journal of the Quekett Microscopical 

 Club. 



The half-yearly volume of this journal contains a de- 

 laif'd list of 140 species of I'Oraminifera, collected by 

 Mr. .Arthur (larland, from the shore-sand at Bognor, 

 Sussex, with four illustration plates, also an illustrated 

 article on the genitation of the Tsetse fly, by Mr. 

 W'.ilter Wesche. Mi". F. P. .Smith contributes a list 

 of all the species of spiders of the Walekciwi'ria group, 

 wliiih \y.\\v occurred in the British Isles, and a descrip- 

 tion 111 .1 spider found at A'armouth, which he believes 

 to be a new species of the Erigone group. The 

 Journal, in accordance with the economic policy of the 

 Club, is iiinsiderablv reduced in size, which is a matter 

 for rep ret. 



R-oyal Microscopicevl Society. 



The .annual meeting w.as held .at 20. Il.anover Square 

 on l.anuary 7, the President, Ur. D. H. Scott, in the 

 chair. Attention was called to a donation from M. 

 Nachet, a Fellow of the Society, of six micro- 

 daguerrotypes of blood, milk, crystals, &c., set in a 

 frame. They were taken with the electric light by M. 

 Leon Foucault in the year 1844, and are probably the 

 oldest of their kind in existence. The photographs are 

 of undoubted excellence, and will compare favourably 

 with many of later date. There was also a donation 

 of 15 slides of the Oribatidse from Mr. N. D. F. Pearce, 

 to supplement the collection presented by Mr. Michael. 

 Some excellent photo-micrographs of diatoms and 

 Podura scale were sent for exhibition by Mr. F. A. 

 O'Donohue. The report of the Council and Treasurer's 

 statement for 1905 were read and adopted, and the 

 n.ames of the officers and Council elected for the en- 

 suing year were announced. Dr. D. H. Scott having 

 been elected as President for a third term. The Presi- 

 dent delivered his annual address, the subject being 

 " The Life and Work of Bernard Renault," illustrated 

 with numerous lantern slides. 



Quekett Microscopical Club. 



.\l the nn-etlng held on |anu.irv iq at 20, Hanover 

 -Square, Dr. \i. J. .Spitta in the chair, ^h•. R. T. Lewis 

 delivered a lecture on " The Senses of Insects," deal- 

 ing more especially with sight and hearing. Compari- 

 son ha\ing been made with the physiology and anatomy 

 of such .senses in man, and stress having been laid upon 

 the important part played by psychological factors, the 

 lecturer explained the theory of " .Sympathetic \'ibra- 

 tions " and its possible applications. It was suggested 

 th.at as insects li\e in the same light and air as man, 

 similar, or, at least, analogous structures should be 

 looked for, but that there was every probability that 

 they were capable of appreciating a far greater range of 

 vibrations of both light and sound, especially in the 

 direction of the shorter wave-lengths. The auditory 

 organs of insects presented a great variety of structure, 

 those of the Orthoptera most nearly complying with 

 what we might expect to find — organs designed to ap- 

 preciate such sounds, for instance, as we might our- 

 selves hear; but their position and number varied con- 

 siderably in different families. It was considered that 

 in addition to sight and hearing insects possessed the 

 sen.scs of taste, smell, and touch, and that some were 

 endowed wth the "sense of direction." Mr. Lewis 

 made an interesting statement regarding the figure in 

 Carpenter reputed to be a reproduction of a photograph 

 made by Exner through an insect's compound eve, call- 

 ing attention to the fact that at ;i meeting of the Royal 



