478 



NA TURE 



[^Marck 20, 1890 



mitter, by Mr. F. B. Hawes. The author exhibited photographs 

 of the interior portions of the transmitter on which the deposit 

 had taken place. These portions consist of a -metal diaphragm, 

 a highly-polished carbon button, and a platinum contact piece 

 carried by a German silver spring placed between them. The 

 diaphragm presented a mottled appearance due to the deposit, 

 but the part which had been behind the German silver spring 

 seemed comparatively clean. The deposits on the carbon button 

 and German silver spring were much less dense than that on the 

 exposed parts of the diaphragm, and the space near the point of 

 contact between the platinum and carbon was free from deposit. 

 The deposit was fairly adherent, some rubbing being neces- 

 sary to remove it, and on examination under the microscope 

 particles of copper and metallic crystals could be seen. The 

 author believes the deposit due to some kind of bombardment 

 of carbon particles, but was unable to say why it should occur, 

 or why the varnished diaphragm should receive the greater 

 deposit although it was further from the carbon than the German 

 silver spring. Mr. C. V. Boys said the photographs reminded 

 him of a phenomenon he observed some time ago on a glass 

 sheet against which one terminal of a dry pile had been resting 

 for some weeks. Just as on the carbon button, the glass near 

 the point of contact was clean and had a comet-shaped deposit 

 formed around it. He could offer no explanation of the appear- 

 ance. — The geometrical construction of direct- reading scales for 

 reflecting galvanometers, by Mr. A. P. Trotter. In a recent 

 paper on galvanometers, by Prof. W. E. Ayrton, F. R.S., 

 T. Mather, and Dr. W. E. Sumpner, read before the Society, 

 the opinion was expressed that proportionality of scale reading 

 to current was very desirable, and the present paper shows how 

 to bend a scale of equal divisions so as to give the required pro- 

 portionality. Suppose the currents required to produce several 

 deflections have been experimentally determined. A full-size 

 plan of the scale is then drawn, and radial lines from the points 

 on the scale at which the observations were taken are drawn 

 towards the centre of the mirror. Let these radii be numbered 

 o, I, 2, 3, &c., commencing from zero azimuth. According to 

 the procedure recommended, distances proportional to the several 

 current strengths are marked off along the edge of a strip of 

 paper, a few inches being left over at each end. Call the marks 

 a, h, c, d, &c., a being the zero point. Two points on the radii 

 o, I, and equidistant from the mirror are now found such that the 

 distance between them is equal to that between a and b on the 

 strip, and the points marked by fine needles stuck in the board. 

 The zero end of the strip is now fixed so that the marks a and b 

 lie against the needles, and the strip is swept round until the 

 mark c coincides with the radius 2, where also a needle is placed. 

 Repeating the process gives a series of points which on being 

 joined form part of a polygon. A line can then be drawn 

 between the inscribed and circumscribing curves which has the 

 same length as the sum of the straight lines, and this is the curve 

 to which the original scale may be bent so as to give proportional 

 readings. Diagrams showing such curves, constructed from the 

 calibrations of instruments given in the paper above referred to, 

 accompany the paper. The author showed that a family of 

 curves may be drawn, each of which satisfies the required con- 

 dition. Of the two limiting curves, one is tangential to the 

 usual scale line at zero azimuth, and the other passes through the 

 vertical axis of the mirror. The flattest of the various curves is 

 generally the most convenient. Mr. J. Swinburne asked whether 

 good definition could be obtained when such curved scales not 

 equidistant from the mirror were used, and also whether it was 

 not easier to divide a flat scale unequally so that the readings are 

 proportional to the current. Mr. Trotter, in reply, said Dr. 

 , Sumpner thought there would be no difficulty as regards definition 

 with the flat curves shown. He (Mr. Trotter) also added that 

 a curved scale might be advantageous in reading the deflections 

 from one side of a table, as the more distant part of the scale 

 could be more nearly perpendicular to the line of sight. For 

 such an arrangement, however, a parallel beam of light would be 

 required, — A parallel motion suitable for recording instruments, 

 ty Mr. A. P. Trotter. This is a modification of Watt's parallel 

 motion, in which the two fixed centres are on the same side of 

 the line described by the "parallel point." The arrangement 

 consists of two vibrating arms, one of which is twice the length 

 cf the other, and whose outer ends are jointed respectively to 

 the niiddle and end of a short lever ; the free end of the latter 

 describes an approximate straight line. The motion was arrived 

 at by considering the curve traced out by a point on the radius 

 of a circle, such that its distance from the circumference measured 



towards the centre is equal to the radial intercept between 

 the circle and a tangent line. The equation to the curve is 

 r — 2 - sec Q (conchoid of Nicomedes) and the radius of the 

 osculating circle at the point where the intercept is zero is given 

 as half that of the initial circle. This osculatory circle, the 

 author finds, practically coincides with the curve over a consider- 

 able angle (40°), and thus may replace this part of the curve ; 

 hence the motion. The author thinks the motion will be useful 

 for recording barometers, ammeters, and voltmeters, as it is more 

 compact than that of Watt, and needs no fixed point beyond the 

 straight path. — Owing to the absence of Prof. S. P. Thompson, 

 his paper on Bertrand's refractometer was not read. 



Linnean Society, March 6. — Mr. Carruthers, F.R.S., Pre- 

 sident, in the chair. — Mr. Thomas Christy exhibited a dried speci- 

 men of Picramnia antidesma, the plant from the bark of which 

 a medicine, known as cascara amarya, a useful alterative in 

 diseases of the blood and skin, is believed to be prepared. — 

 Mr. J. E. Harting exhibited a series of horns of the American 

 Prongbuck {Antilocapra americana), to illustrate the mode 

 in which the shedding and new growth of horn is effected 

 in this animal. — A paper was read by Mr. D. Morris, on the 

 production of seed in certain varieties of the sugar-cane {Sac 

 charum ojfficinarum). It was pointed out that, although well 

 known as a cultivated plant, the sugar-cane had nowhere been 

 found wild; 'nor had the seed {caryopsis) been figured or de- 

 scribed ; it being the generally received opinion that, having 

 been propagated entirely by slips, or cuttings, it had lost the power 

 of producing seed. Spikelets, however, received at Kew, had 

 been carefully examined, and the seed found, which was now 

 for the first time exhibited by Mr. Morris. He anticipated that, 

 by cross-fertilization and selection of seedlings, the sugar-cane 

 might be greatly improved, and much importance was attached 

 to the subject, as it opened up a new field of investigation in 

 regard to sugar-cane cultivation. Mr. J. G. Baker and Mr. Christy 

 concurred. — A paper was then read by Mr. Spencer Moore, 

 on the true nature of callus ; Part i, the vegetable-marrow and 

 Ballia callitricha. It was shown that the callus of sieve-tubes 

 of the vegetable-marrow gives marked proteid reactions ; and 

 since it is dissolved in a peptonizing fluid there can be no doubt 

 of its being a true proteid, and not a kind of starchy mucilage, 

 as is usually supposed. The "stoppers" of Ballia also yield 

 proteid reactions, but inasmuch as they resist gastric diges- 

 tion, the substance cannot be a true proteid, and may perhaps 

 be allied to lardacein. Mr, Moore maintained the view of 

 Russow, Strassburger, and others — that callus is deposited upon 

 the sieve — to be correct in the case of the vegetable-marrow ; 

 since a peptonizing fluid clears the sieve-plates and leaves them 

 in their pristine condition, which would not be the case if callus 

 were formed by a swelling up of the sieves. A discussion fol- 

 lowed, in which Dr. F. W. Oliver, Dr. D, H. Scott, Prof. 

 Reynolds Green, and Mr. George Murray took part. 



Zoological Society, March 4. — Prof. W. H. Flower, 

 F.R. S., President, in the chair. — The Secretaiy read a report 

 on the additions that had been made to the Society's Menagerie 

 during the month of February 1890. — Mr. F. E. Beddard ex- 

 hibited and made remarks on some living specimens of an Indian 

 Earthworm {PericJiceta indica), obtained from a greenhouse in 

 Scotland. — Mr. A. Thomson exhibited a series of insects reared 

 in the Insect House in the Society's Gardens during the past 

 year, and read a report on the subject. Particular attention was 

 called to specimens of a South African Mantis {Harpax ocellata) 

 and of a Canadian Stick Insect {Diaphemora femoratd). — Mr. 

 Henry Seebohm read a paper on the classification of birds, being 

 an attempt to diagnose the sub-classes, orders, sub-orders, and 

 some of the families of existing birds. The characters upon 

 which the diagnoses were based were almost entirely derived 

 from points in the osteology, myology, and the pterylosis of the 

 groups diagnosed. — A communication was read from Mr. T. D. 

 A. Cockerell, describing some Galls from Colorado, of which 

 specimens were transmitted for exhibition. 



Edinburgh. 

 Royal Society, February 28. — Sir Douglas Maclagan, Vice- 

 President, in the chair. — Prof. Rutherford communicated a paper 

 on the structure and contraction of striped muscular fibre of 

 crab and lobster. — Prof. Haycraft read a paper on the histology, 

 functions, and development of the carapace of the Chelonia, 

 and also another paper on the rate at which muscles contract : 

 when the motor paths are stimulated by interrupted electrical j 

 currents. t 



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