22 



KNOWLEDGE & SCIENTIFIC NEWS. 



[January, 1907. 



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



Royal Microscopical Society.. 



.\u\ii.\iui;u Ji, Mr. A. .\. DLsnox , .M.A., 15. Sc, in llic 

 chair. The Curator described two old microscopes 

 which had been pre.scntcd to the Society's collection. 

 One was a Ciilpeper microscope of early 18th century 

 date, presented by Mr. Wynne 1'^ IJaxtcr; the other, of 

 late i8lh century date, was made by Dolland, after 

 Cull's model, and was presented bv Mr. C. Lees Curties. 

 Dr. Uebb exhibited a new porcelain filter, made by 

 Doulton and Co., suitable for laboratory work, and he 

 also exhibited for Mr. Taverncr a sm;dl filter bottle 

 for filtering micro mounting fluids. Mr. Conrad Beck 

 exhibited an optical bench for illumination with either 

 ordinary or monochromatic light, arranged to show 

 experimentally that A. pcUiicida could be resolved by 

 green light, when, under the same conditions, yellow- 

 light failed to resolve it. Messrs. Zeiss exhibited a 

 special microscope for photo-micrography of metallurgi- 

 cal specimens. Mr. J. W. Gordon gave a summary of 

 his paper, " On the Use of a Top Stop for Developing 

 Latent Powers of the Microscope," and exhibited his 

 ajiparatus, pointing out that a top stop admits of varia- 

 tion between the proportion of the refracted and un- 

 relracted light which passes the instrument, and thus 

 renders more conspicuous a particular feature of the 

 object. In illustration, he exhibited photographs taken 

 with an achromatic oil-immersion lens of N.A. i.o, 

 which were designed to show how, by means of a top 

 stop, an objective of this aperture might equal the per- 

 formance of an objective of much wider aperture. Mr. 

 Rheinberg contended that the use of a stop in the 

 Ramsden circle of a microscope was, from an optical 

 point of view, equivalent to the use of a stop in the 

 upper focal plane of the objective, and that the use of 

 a stop which puts out of use the central portion of an 

 objective deteriorates and falsifies the image. Mr. 

 Conrad Beck observed that if the course of the rays 

 were followed, it would be found that there was but one 

 ]>oint through which all the rays passed symmetrically, 

 and that was in the Ramsden circle, so that this was the 

 best place for the insertion of a patch stop, and he con- 

 troverted Mr. Rheinberg's view that the jiutting of a 

 .stop in the posterior focus of the lens gave the .same 

 results. Mr. Conrady said Mr. Gordon had repeated 

 his idea that the well-known visibility of single minute 

 objects proved the accepted limits of resolution to be 

 wrong, and laid stress on the fact that mere visibility 

 and resolution were totally different things, the former 

 being merely a question of contrast, an object, however 

 small, beings seen if it contrasted sufficiently with its 

 background. Stars that were probably below ,,',„ of a 

 second in arc in apparent size were visible to the naked 

 eye, which had a limit of resolution of about 60 seconds, 

 and we had here visibility of objects measuring less 

 than 3000 part of the least distance at which two such 

 objects could be separated and resolved. He con- 

 sidered the delicate tracing on diatoms referred to by 

 Mr. Gordon to be spurious appearances of the 

 intercostal order. Mr. Gordon brieflv replied, agreein"- 



with Mr. Rheinberg's statement that a top stop in the 

 Ramsden disc was equivalent to a stop placed in the 

 upper focal plane of the objectixe, subjict to Mr. Beck's 

 criticisms, and to the fact that the wave fronts were 

 plane in the former position and sj)herical in the latter. 

 Quekett Microscopical Club. 



.\o\enilici' i(). A p.ipei 1)\ Mr. 1'. I'. .Smilli, on 

 " The Classification of the British .Spiders ol the genus 

 l.ycoso," was taken as read. Mr. ]''. P. .Smith gave a 

 lecture on "Vagabond .Spidirs. " He said that the 

 more highly specialised forms of sjjiders fell pretty 

 n.ituiallv into two groujis, the first — probably deriva- 

 tives ol the genus Fac/iygiiatlia — including all those 

 species which made either orbicular, " saucer," or 

 " tangle," snares, and second, those which constructed 

 no snare at all. The three principal groups of vaga- 

 bond (wimdering) spiders were represented by the 

 typical families Lycosid;e, Thomisidie, and Salticidae. 

 The females of the genus Lycosa carry the egg-sac about 

 attached to the spinners, and the young, w hen hatt-hed, 

 live for some time upon the back of the mother. 

 Spiders of the genus Piraia are al)le to- run u]Km the 

 surface of water, and Dolomcdcs constructs a raft and 

 makes considerable voyages. The Crab-spiders (Thomi- 

 sid;e) have a peculiar articulation of tlie legs which 

 enables them to travel forwards, sideways, or back- 

 wards with equal facility. A short description was 

 given of the more striking characteristics and habits of 

 the Salticida;, of which there are some 33 British species 

 at present known. The lecture was illustrated with a 

 number of especially interesting lantern slides, some of 

 " face " views of spiders, producing not only a striking 

 effect, but demonstrating clearly the arrangement of 

 the eyes, and was concluded w ith a series of five photo- 

 graphs showing the attack upon, and capture of, a 

 house fly by JMarpcssa iniiscosa. 



Microscope Slidos. 



Mr. H. W. H. Darlaston, of 20, Freer Road, Birch- 

 field, Birmingham, has sent me particulars of a some- 

 what novel method of circulating slides. Briefly the 

 arrangement is that for a subscription of two guineas, 

 600 slides will be sent, post paid, in 12 monthly parcels 

 of 50 slides each. From each monthly parcel five 

 slides, 60 in all, may be selected and retained by the 

 subscriber free, and he may also select further slides at 

 an all-round price of 6d. each. For a subscription of 

 one guinea, 25 slides per month will be sent, and two 

 per month retained, whilst for half a guinea twelve 

 slides per month are sent, and one per month retained. 

 Of the slides sent me as specimens I can speak highly; 

 they are beautiful examples Oif the mounter's art, and 

 in no way inferior to slides sold at double the price. 

 Microscope Material. 



By the kindness ol Mr. lirnest Heath, of Cardiff, I 

 am able to offer for distribution to my readers a con- 

 siderable quantity of anchor mud and dredger sand 

 from the Adriatic. Mr. Heath says : " I made these 

 gatherings myself, and a friend sent me a great many. 

 They extend over a fairly wide area on the eastern 

 coast from Trieste to Spalato. Your readers will, I 

 think, find them very rich in I'^oraminifcra and MoDusca, 

 but the diatoms I expect I have pretty well washed out 

 in getting my own floatings. There is a very wide 

 range of L'oraminifera and abundant beautiful speci- 

 mens of PcHcroplis planalns. I have also had some very 

 curious and abnormal specimens of Polymorphina. The 

 Adriatic is one of the richest seas in Foraminifera. I 

 was bathing from the shore on one of the Brioni Islands, 

 and as I walked into the sea the sand rose up and 

 floated around my legs in clouds, just the same as one 



