48 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Mar., 1904. 



by means of a thumb screw only. It is decidedly original in 

 design. .\ friction wheel, actuated by a single milled head, is 

 in contact with a broad brass plate attached to the clips which 

 hold the slide. A steel spring gives the necessary pressure, 

 and the spindle bearing the friction wheel and milled head is 

 movable on a vertical pin. A glance at the illustration will 

 make the principle clear, and it will be seen that the stage 



S^^^j 



BOjI 



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T* 



travels readily m a \ertical or horizontal direction, or in any 

 intermediate diagonal direction, according to the position in 

 which the milled head is held whilst rotating. Check pins in- 

 dicate the horizontal and vertical positions respectively. By 

 this means not only are rectangular movements obtained, but 

 any desired diagonal movement is obtained in addition. The 

 whole stage works with great smoothness and sensitiveness. 

 The mechanism is entirely on one side of the stage, so that 

 none of the working parts are in the way of the instrument. 



Quekett Microscopical Club. 



The 409th ordinary meeting of the Club was held on Decem- 

 ber is. at 20, Hanover Square, W., the Vice-President, A, D, 

 Michael, Esq., F.L,S., in the chair, A most interesting col- 

 lection of diffraction gratings of various kinds was on view, 

 and the exhibitor, Mr, Julius Rheinberg, F,R.M.S,, briefly 

 described them and pointed out the curious optical effects 

 obtainable. Among the most interesting of the exhibits was 

 a reflecting diffraction grating on plate glass, silvered on the 

 grating side, ruled by Colonel L. Paxton, of Chichester, It 

 consisted of intersecting systems of circles. Each system 

 consisted of a series of excentric circles, the locus of their 

 centres being an intermediate circle. When exposed hori- 

 zontally below a flame, an observer stationed a few yards 

 away could see four intersecting rings of light stereoscopically 

 projected several inches in front of the mirror, whilst a 

 similar system of rings was seen several inches behind the 

 mirror, 



Mr, Rheinberg then read a paper ''On an Overlooked Point 

 concerning the Resolving Power of the Microscope." It dealt 

 with a discovery made from the theoretical standpoint some 

 years ago by Dr. Johnstone Stoney, F,R.S,, which had only 

 recentlv been practically demonstrated — viz., that an objective 

 would resolve and separate two dots or Imes of a known 

 distance apart, although unable, owing to its N,.\,, to resolve 

 a series or band of dots or Hues at equal similar intervals. 

 The experiment was practically demonstrated to the Club, a 

 Grayson test plate of 15,000 lines to the inch being used for 

 the purpose, with a Zeiss S mm, apochromat. and a 27 mm. 

 compensating ocular. 



Mr. D. J. Scourfield, F.R.M,S,, then gave an epitome of the 

 third part of his Synopsis of the British Fresh Water Entomo- 

 straca. It dealt with the ( Jstracoda, of which we have about 

 62 species, nearly all widely distributed ; the Phyllopoda, of 

 which there is only a single form now recorded, another form, 

 .•l/j».s£((Hi-n/o>-;«/s,being apparently extinct: and the Branchiura, 

 with two species, one lieing extremely rare. This was the con- 

 cluding portion of Mr, Scourfield's valuable series of papers 

 on the British Entomostraca, 



The 410th ordinary meeting of the Club was held on 

 January- 15, the President, Mr,-(ieorge Massie, F,L,S,, in the 

 chair. There was a large attendance, Mr, C, Rousse- 

 let, F.K.M.S., read a paper ou '■.\ New Freshwater Poh'zoon 

 from Rhodesia," which was illustrated both by a diagram and 

 by specimens shown under the microscope. The polyzoon 

 referred to differs in many ways from all other known species, 

 and is especially characterised by the production of elliptical 



statoblasts having five spines at each end, the spines being 

 armed with minute hooks, 



Mr. J. T. Holder exhibited an interesting series of lantern 

 slides of Foraminifera from photographs taken by himself. 

 The specimens varied much in size, some of the large groups 

 being J inch in diameter, and containing several hundred 

 selected specimens from -jifj to i inch in diameter. .\ 4-inch 

 objective was used, and in spite of the difference in focal plane 

 the photograph was quite successful. Other photographs were 

 taken with 2-inch and i-inch objectives. The exposures varied 

 from a few seconds to three quarters of an hour, an isochro- 

 matic screen being invariably used. The camera and ap- 

 paratus emploved were also shown on the screen. 



Mr. Earland ga% e a brief description of the slides, and con- 

 gratulated Mr, Holder on his success, and especially on the 

 way in which the glassy transparency, which was one of the 

 most beautiful features of the hyaline Foraminifera, had been 

 reproduced in the photographs. .'Attention was particularly 

 drawn to Frondicutaria aluta from Cuba, found at the depth of 

 700 fathoms. The genus was now almost extinct, but was 

 abundant in Secondary times. .\t present it was found in 

 numbers in only two small areas in the world, each widely 

 distant from the other, namely, the Caribbean Sea and the 

 shores of New Guinea. .Attention w-as also called to the great 

 difference in the form and structure of the specimens shown 

 on the screen. This was due to the different methods of 

 growth, which, in turn, w-as a result of the difference in size of 

 the primordial chambers. It was a typical instance of dimor- 

 phism, and the two specimens represented the megalospheric 

 and microspheric types respectively. Two especially interest- 

 ing slides were Polystomella craticiilata and Orhulina uiiii-ersa. 

 In the first the foraminifer was show-n side by side with 

 a cast of the animal's body, the cast being quite perfect, 

 and exhibiting every detail of structure, the canal system 

 and primordial chamber being sharply marked on the 

 screen. In the slide of Orhulina iinivirsa some of the 

 spherical details had been laid open in order to show 

 the internal Globigerina shell. This was shown in various 

 stages, from the perfect shell, attached by five spines to the 

 inner surface of the sphere, and not distinguishable from a 

 pelagic Globigerina, to the last disappearing chamberlet. The 

 mystery of these internal chambers, which were only found in 

 a small percentage of specimens, was unsolved ; but a theory 

 had been invented to account for them. It was supposed 

 that the pelagic Globigerina, in order to protect its delicate 

 spinous shell from the action of the waves, formed a spherical 

 shell outside it, and the internal shell being then of no further 

 use was gradually absorbed ind disappeared. A number of 

 photographs of rock-sections next exhibited showed Foramini- 

 fera ill situ, and exemplified the important part played bv 

 them in the structure of the earth, more important than all 

 other animals put together. They were amongst the very 

 earliest inhabitants of the earth, their remains being found as 

 far back as the Lower Cambrian strata, and some of the 

 genera, perhaps even species, found there were still in exis- 

 tence. They formed enormous masses of limestone in carboni- 

 ferous times, and the gault and chalk were largely composed 

 of their remains. But they reached their greatest develop- 

 ment in Tertiary times, when the famous Nummulitic and 

 .\lveolina limestones were built up by them, the deposits 

 stretching in an almost unbroken series across Europe and 

 the western half of Asia, reaching a thickness in places of 

 many thousand feet. Their modern representatives were both 

 small and infrequent. 



In addition, a number of marine organisms, admirably pre- 

 served, were shown under microscopes on behalf of Mr, H, J, 

 Waddington, a former member of the Club, 



Royal Microscopic.\l Society, December 16, Dr. Henry 

 Woodward. F,R,S,, President, in the chair. Mr. F, W, Watson 

 Baker exhibited under microscopes an exceedingly complete 

 and valuable series of slides, 16 in number, illustrating the 

 development of an ascidian from the fertilization of the ovum 

 to the larval stage. The slides were prepared by a gentle- 

 man well known to many of the Fellows, who had been 

 most successful in his management of marine aquaria. Dr. 

 G. J. Hinde read a paper " On the Structure and .^.ffinities of 

 the Genus Pomsphara." which was illustrated by diagrams, 

 mounted slides under microscopes, and specimens, many col- 

 lected by Dr, Hinde in his garden at Croydon, which had 



