January 7, 1892] 



NATURE 



239 



*' inductance " should mean L/, but Mr. O. Heaviside, who 

 introduced the term, had used it for L. The President re- 

 marked that some time ago Dr. Sumpner and himself felt the 

 need of a name for L/, anl thought of using " inductance." but 

 on referring to Mr. Heaviside's articles found it used for L. 

 Dr. C. V. Burton asked whether the word "self-induction" 

 could not be used as an abbreviation for " coefficient of self- 

 induction." Dr. Thompson pointed out that this word already 

 had a meaning, viz. L multiplied by current. Dr. Burton then 

 suggested that inductivity might be applicable. Dr. Thompson 

 said the word " impedance" was also used ambiguously, for the 

 sense in which Dr. Lodge uses it in his "Modern Views of 

 Electricity" is not the same as the vector sum of R and L/. 

 Prof. Perry recalled the fact that "impedance" had been 

 defined by the Committee of the British Association as the 



effective voltage t-. t'i. -j .1 • j c • • 



ratio „ "" . Dr. Thompson said this definition was 



effective current 

 only applicable to periodic currents, and not to intermittent or 

 transient ones. The President said he understood the first 

 object of Mr. Kilgour's paper was to inquire whether the dread 

 of rise of voltage occurring when concentric mains were used 

 need exist. When Dr Fleming's paper was read, the general 

 idea was that concentric cables were dangerous. In the dis- 

 cussion on it, he, amongst others, had pointed out that the 

 chance of a large rise of pressure was not a serious one. Mr. 

 Kilgour had now shown that the range of capacity over which 

 a particular rise could occur is inversely proportional to the 

 maximum rise possible in the particular circuit. When the 

 circuit was such that a large rise was possible, the probability of 

 any serious rise taking place was very small, hence the fears of 

 large rises were more or less unfounded. The second part of the 

 paper was to show that ordinary problems on concentric cables 

 could, in practice, be treated with sufficient accuracy by 

 assuming the capacity localized at either end of the cable, 

 instead of distributed along its length. 



Royal Microscopical Society, December 16, 1891. — 

 Dr. K. Braithwaite, President, in the chair. — Mr. E. M. 

 Nelson said he had severely tested Messrs. Powell and Lealand's 

 new apochromatic iV of 1'4 N.A. both visually and photo- 

 graphically, and he could say it was of remarkably fine glass. 

 It gave an imTge more free of colour than that of many apochro- 

 matics he had seen ; its speed in microphotography was very 

 great. He noted it was fitted with a correction collar. — Mr. H. 

 Bernard exhibited and described a new form of mechanical 

 stage which he had invented ; it was specially designed to 

 obviate the inconvenience arising on account of the very limited 

 range of motion admitted by those at present in use. The 

 plan which he had tried to follow was to imitate the movement 

 of the fingers as they are used for moving glass slides under the 

 microscope. The mechanism was all under and at the side of 

 the stage. Slides were moved by light adjustable frames. In 

 this way a movement of 10 cm. by 5 cm. was speedily obtained 

 without jarring against the condenser, or interfering with the 

 light. Large slips with series of sections could thus be very 

 easily examined, and zoophyte troughs could be searched from 

 corner to corner. By placing a brass plate on the movable 

 frame it was shown that the contents of a watch-glass could be 

 closely examined, the movement avoiding the usual shaking of 

 the fluid caused when watch-glasses are manipulated by 

 the fingers. He had shown the original drawings of the stage 

 to Prof. Abbe, who thought the idea was so good that he 

 had had the stage exhibited made by the firm of Zeiss. The 

 President, in thanking Mr. Bernard for bringing this stage to 

 their notice, expressed the opinion that it was likely to be founi 

 most useful for dissecting purposes. He had often felt l.-o 

 inconvenience arising from the want of a greater range of move- 

 ment in the ordinary mechanical stage. After the business of 

 the meeting was over, Mr. Bernard gave a demonstration to the 

 Fellows, and very favourable comments were passed on its 

 practical use and originality. — Prof. J. W. Groves read a letter 

 from Mr. Hermann giving information that Volvox globator ^2,% 

 to be found in great abundance in a pond in the neighbourhood 

 of Balham. — A paper on the resolution of Podiira, by the Hon. 

 J. G. P. Vereker, was read by Prof. Groves. The author stated 

 that he had been experimenting in photomicrography on some 

 scales of Podura, and had obtained results which he thought 

 threw some liijht upon their structure. The photomicrographs 

 exhibited he considered appeared to prove that the Foditra 

 scale consists of a hyaline beaded membrane, having minute 

 featherlets inserted in it. At the broadest part of the scale 



NO. II 58, VOL. 45] 



there are one or two rows of beads between the featherlets, 

 while towards the base and top of the scale the beads tend to 

 form single rows. Mr. E. M. Nelson believed that the effects 

 were due to the thickening of the membrane. Mr. J. E. Ingpen 

 said that Mr. Wenham had gone into this subject, and he hal 

 come to the conclusion that the markings were inflations of the 

 membrane. — The President reminded the Fellows that the next 

 meeting would be the anniversary, and that it would therefore 

 be necessary to appoint two auditors to examine the treasurer's 

 accounts; on behalf of the Council he had appointed Mr. W. 

 T. Suffolk. Mr. Nelson proposed, and Mr. Wynne E. Baxter 

 seconded, Mr. J. M. Allen as auditor on the part of the Fellows. 

 This was put to the meeting and unanimously carried. 



Edinburgh. 



Royal Society, December 21, 1891. — Dr. William Craig 

 in the chair. — Prof. Crum Brown communicated an obituary 

 notice of the late Mr. Andrew N oung, by the Rev. Prof. Flint. 

 — Prof. Crum Brown also read a preliminary communication, 

 by Dr. Dawson Turner, on the electric resistance of various 

 urines. The electric resistance is found to vary markedly when 

 the proportion of solid constituents in solution is different. 

 This test promises to be of use to the medical practitioner. 

 Kohlrausch's method of determining the resistance by alternating 

 currents and the telephone was adopted. — Mr. Malcolm Laurie 

 read a paper on some Eurypterid remains from the Upper 

 Silurian deposits of the Pentland Hills. This collection of 

 fossils is now in the Edinburgh Museum of Science and Art, 

 and contains a number of new forms, one of which has been the 

 type of a new genus — Drepanopterus. This form is charac- 

 terized by great breadth of carapace, and by the form of the 

 single limb which is preserved. The limb is long and narrow, 

 and ends in a slightly expanded sickle-shaped segment. The 

 genus appears to occupy a position intermediate between 

 Eurypterus and Stylomiriis. Among the other remains are 

 found two new species of Stylonttrus — 3". ornatus and S. 

 macrophthalmus. Two new species of Eurypterus are also 

 represented—^, conicus and E. cyclophthalmus . The second 

 species of Stylonurus and both species of Eurypterus are charac- 

 terized by exceptionally large eyes. — Prof. Cossar Ewart read the 

 second part of a paper, written by himself and Mr. J. C. 

 Mitchell, on the lateral sense-organs of Elasmobranchs. In 

 this part the authors dealt with the sensory canals in Raia 

 batis. It has been supposed that these canals serve for the 

 production of mucus. The authors consider that this idea must 

 be abandoned. They have observed a number of mucus glands 

 in the skin sufficient to account for all the mucus found on the 

 surface. They incline to the opinion that the canals have some 

 respiratory function. 



Paris. 



Academy of Sciences, December 28, 1891. — M. Duchartre 

 in the chair. — On a telescope reseau, by M. Mascart. — Note, 

 by M. Faye, accompanying the presentation of the Annuaire 

 du Bureau des Longitudes for 1892. — On the number of roots 

 common to several simultaneous equations, by M. Kronecker. — 

 Another note on the same subject, by M. mile Picard. — On 

 the glycolytic and saccharifying powers of the blood in hyper- 

 glycemic asphyxia, in phloridzic diabetes, and in the diabetes of 

 man, and on the localization of the saccharifying ferment in 

 the blood, by MM. R. Lepine and Barral. — Note on the dif- 

 fraction effects produced by screens placed in front of photo- 

 graphic and ordinary object-glasses, by Prof. Pritchard. (See 

 Our Astronomical Column.) — On conjugate systems with equal 

 invariants, by M. G. Kcenigs. — On the theory of linear differ- 

 ential equations, by M. Andre Markoff. — Complement to one 

 of Abel's problems, by M. Bougaieff. — On a new spectrometer 

 {rifraclomitre), by M. C. Fery. The principle upon which the 

 instrument has been constructed consists in annulling, by a 

 solid prism of variable angle and constant index of refraction, 

 the deviation produced by a hollow prism having a constant 

 small angle, and filled with the liquid whose refractive 

 index is required. To realize these conditions, a pris- 

 matic-shaped cavity has been cut out of a double-convex 

 lens in a plane perpendicular to the axis. This cavity is 

 filled with the liquid under examination. And since, in a 

 lens, the angle formed by the plane tangents to the surfaces of 

 curvature is sensibly proportional to the distance from the optical 

 centre, the angle of the lens considered as a prism can be varied 

 by motion in a plane perpendicular to the axis. The amount 

 of lateral motion necessary to bring about no deviation, when 



