May 28, 1896] 



NATURE 



93 



(c) An average rate of discharge of 3 to 4 per second. 



(d) A susceptibility to fatigue showing itself in the discharge fail- 

 ing after it had recurred from two to five times at the above rates. 



Physical Society, May 22.— Prof. Ayrton, Vice President, 

 in the chair. — Mr. K. Appleyard read a paper on dielectrics. 

 The author has particularly investigated the effect of temperature 

 on dielectric resistance. He has employed for this purpose con- 

 densers insulated with mica and p.iraflined paper. In order to 

 eliminate some of the effects of surface leakage. Price's guard- 

 ring arrangement was made use of in all the experiments. The 

 author finds that the capacity of a paraffin condenser varies 

 irregularly with the temperature, but lliat to within the accuracy 

 attainable with his instruments (i per cent.), the capacity of a 

 mica condenser is constant between 11' F. and 110° F. If the 

 resistance of parafiTin at a temperature / is represented by 

 K/ = Ro', the mean value for log a deduced from all the 

 author's measurements is I'96344. Experiments made with a 

 parallel plate condenser with paraffin as the dielectric, show that 

 when the temperature reaches within about 20° of the melting 

 point the resistance rapidly falls ; when melting commences 

 there is a rapid drop, but while melting is in progress the resist- 

 ance remains constant. Prof. Ayrton said he could bear witness 

 to the extreme value of Mr. Price's device, as it completely did 

 away with the necessity for the extreme care previously necessary 

 to prevent errors due to surface leakage. He regretted that he 

 had not had an opportunity of comparing the author's numbers 

 with some obtained some years ago by Prof. Perry and himself 

 (Prof Ayrton).^A paper by Prof. Viriamu Jones, on the mag- 

 netic field due to an elliptical current at a point in the plane of 

 the ellipse and within it, was taken as read. Prof Silvanus 

 Thompson said that this paper was of interest not only on 

 account of the application which others might make of the 

 author's method, but also in that the correction when applied to 

 Prof Jones's results brought the international ohm more nearly 

 into accord with the true ohm. Mr. J. J. Walker said he con- 

 sidered that the paper was more suited to the Mathematical 

 Society. The integration which the author reduced to elliptic 

 integrals might be more easily performed by another method. 

 Prof Ayrton said that Prof. Jones's value for the true ohm was 

 now lo6'302 cm. of mercury. — Mr. Campbell read a paper on 

 new instruments for the direct measurement of the frequency of 

 alternating or pulsating electric currents. The author employs 

 two arrangements, in one of which a steel wire, the tension on 

 which is variable, and the other a steel spring of variable length, 

 clamped at one end, are acted upon by an electro-magnet, 

 through which the periodic current is passed. The tension or 

 length, as the case may be, is varied till maximum resonance is 

 obtained, a small contnct piece being employed to detect when 

 this occurs. The instrument exhibited was capable of measuring 

 the frequency of periodic currents of from 40 to 150 double 

 vibrations per second. Mr. Watson said he thought that in the 

 case of the steel spring there would be a considerable tempera- 

 ture correction, and he suggested a method by which this might 

 be compensated. Mr. Blakesley asked if the author had found 

 that the spring became magnetised and thus gave the octave. 

 Mr. Carter asked whether elastic fatigue influenced the results, 

 and said that a synchronous motor and a speed indicator could 

 be used to measure the frequency. Prof Silvanus Thompson sug- 

 gested that it might be prelerable toeniploy a polarised apparatus, 

 since to avoid the impression of forced vibrations on the spring 

 it was better, as was dime in the case of tuning-forks, to make it 

 massive. It had been found in other cases, such as in Hughes' 

 telegraph and the telephone,' that beiier results were obtained 

 with polarised apparatus. He (Prof. Thompson) had used a 

 telephone, placed anywhere near a magnet traversed by the 

 periodic current, together with a tuning-fork, which gave beats 

 with the note produced by the telephone, to measure frequencies. 

 The variations in frequency ordinarily met with in practice were 

 much greater than was generally suspected. Mr. Blake.sley said 

 he considered that the advantage of the author's instrument over 

 a telephone and tuning fork was that it was continuously vari- 

 able over a large range. Mr. Enright asked if the author had 

 been troubled by the spring or wire breaking into overtones. In 

 some experiments in which rather long wires were used, he had 

 been troubled in this way. Prof Ayrton said that he did not 

 think that it was possible to get the wire or spring to respond to 

 the octave unless the alternating current contained a component 

 of the fre(|uency of the octave ; in fact, he had himself used such 

 a stretched string as a wave analyser. I le had used a telephone 

 to prove thai the note given by a hissing alternate current arc 



NO. 1387, VOL. 54] 



corresponded in frequency to that of the current. In the in- 

 strument used by Prof. Perry and himself, a polarised arrange- 

 ment was always employed, since the alternating current was 

 passed either through a wire in a constant magnetic field, or 

 through an electro-magnet which acted on a wire through which 

 a constant current was passed. The author, in his reply, said 

 that the instrument responded, though feebly, to the octave, and 

 this response might be made use of to check the accuracy of the 

 scale. — The .Society then adjourned till June 12. 



Entomological Society, May 6.-— Prof. Meldola, F.R.S., 

 President, in the chair. — .Mr. Champion exhibited specimens 

 of Amaru fainelica, Zimm., from Woking, Surrey, a recent 

 addition to the British list. He also exhibited, on behalf 

 of Mr. Dolby-Tyler, a series of Ebiiria quadrinotala, Latr., 

 from Guayaquil, Ecuador, showing variation in the number of 

 the raised ivory-white lines on the elytra. — Mr. Horace Donis- 

 thorpe exhibited a specimen of Pterostichus gracilis with three 

 tarsi on one leg, taken near Weymouth last April. — Mr. G. T. 

 Porritt exhibited a series ofArctia menthrastri which he had just 

 bred from Morayshire ova ; the ground-colour of the specimens 

 varied from the usual white, through shades of yellosv, to dark 

 smoky-brown. — Mr. .Merrifield exhibited specimens of Gon- 

 epteryx rhantni bred from larva; found in North Italy and 

 (iiermany, the pupce of which had been subjected to various 

 temperatures. He stated that high temperature appeared to 

 cause an increase of yellow scales in the female, and low tem- 

 peratures generally reduced the size of the orange discal spot on 

 the forewings of both sexes. — Mr. Merrifield said that the effects ' 

 on the imago produced by temperature were being made the 

 subject of systematic research by Prof Weismann, Dr. Standfuss, 

 Mr. E. Fischer, and others. — Mr. Kirkaldy exhibited and made 

 remarks on ova of Nolonecta glaiica var. fttrcata. — Mr. Tutt 

 exhibited living larva; of Apamea ophiogramma, together with 

 the grass on which it was feeding. — Sir. Goss read a communi- 

 tion from Mr. E. Meyrick on the subject of Prof. Radcliffe- 

 Grote's criticisms, contained in his paper published in the 

 Proceedings of the Society, 1896, pp. x. -xv. , on the use of 

 certain generic terms by Mr. Meyrick in writing on the 

 Geometridce. — Mr. McLachlan opened a discussion as to the 

 best means of preventing the extinction of certain British butter- 

 flies. He referred to the extinction of Chrysoplianiis dispar, 

 Lyciena acis, and Aporia cralicgi, and to the probable extinction, 

 in the near future, oi Papilio niachaon^ Meliitea cinxia^ and Lyctsna 

 arion. He stated that one of the objects he had in view in bring- 

 ing this matter forward was to see whether some plan could not be 

 devised to protect those specially localised species which were 

 apparently in danger of being exterminated by over-collecting. 

 — Prof. Meldola said he fully sympathised with the remarks of 

 Mr. McLachlan, and thought that a resolution passed by the 

 Society, possibly in conjunction with kindred .Societies, might 

 produce some effect. Mr. Goss stated that Papilion machaon, 

 although apparently doomed to extinction in its chief locality in 

 Cambridgeshire (Wicken Fen), would probably linger on in the 

 country in smaller fens, such as Chippenham, where the larvse 

 had been found feeding on Angelica sylvestris. It would certainly 

 survive in the Norfolk Broads, both from the irreclaimable 

 nature of the fens there and the extensive range of the species in 

 the district. He stated that Melihca cinxia, although gradually 

 disappearing from most of its old localities in the south of the 

 Isle of Wight, was still found in the island further west, where 

 he had seen it in numbers in May 1S95. He added that 

 Lyciena arion was far from extinct in Gloucestershire, and was 

 distributed over a much wider area in the extreme south-west of 

 England than was generally supposed. — Mr. Elwes stated that 

 L. arion formerly occurred in several places on his own property 

 in Gloucestershire, but had disappeared of late years, 

 although not collected. Its disappearance was probably due 

 to changes of climate. — Colonel Irby said that L. anon 

 had disappeared many years ago not only from Barn- 

 well Wold, Northamptonshire, but from another part of the 

 county, on the estate of L.jrd Lilford, not accessible to the 

 public, and that its disappearance there was no doubt caused by 

 the destruction of the food plant and other herbage by burning 

 the pasture, and by the grazing of sheep. Mr. Crowley, 

 Mr. Tutt, Mr. Waterhouse, and Mr. Blandford continued 

 the discussion. — Mr. Guy A. K. Marshall communicated 

 a paper entitled " Notes on Seasonal Dimorphism in South 

 African Rhopalocera.'' — Mr. P. Cameron communicated a paper 

 entitled " Descriptions of new species of Hymenopterafrom the 

 Oriental Region." 



