November io, 1898] 



NA TURE 



47 



some cases sectors upon the second glass to increase the capacity. 

 The output was increased, but the construction lost simplicity. 

 The indifference of Mr. Pidgeon's machine to dirt and dust was 

 1 most valuable result. Mr. Pidgeon, in reply, showed a set of 

 secondary inductors such as Captain Thomson had just pro- 

 posed. They improved the output by about 15 per cent. , but 

 they were troublesome to keep in order, for they increased the 

 tendency to "reverse." — Dr. S. P. Thompson then repeated an 

 'experiment discovered by Prof. Righi, on a magneto-optic 

 phenomenon. It was originally described in Roiiux, K. Aciad. 

 ' Limei, Atti 7, sei: 5, 1S9S. A substance absorptive of light 

 'is submitted to a powerful magnetic field between the pole- 

 pieces of an electro-magnet. The pole-pieces are drilled so 

 that a beam of light from an arc-lamp can traverse the gap 

 'itlon^ the magnetic lines. A polarising prism is placed between 

 the arc-lamp and the electro-magnet. After having passed 

 'through the magnetising apparatus, the beam thus polarised is 

 examined by an analyser. The analyser must be turned to 

 '"extinction" before the magnetising current is turned on. 

 If this is done, brightness is restored at the analyser as 

 soon as the magnetic field is established. The substance 

 absorbing the light in the gap may be nitric oxide fumes, or an 

 'ordinary spirit-lamp sodium flame. The second effect to be 

 'noticed is that when the emergent beam is examined, there is a 

 'splitting of the lines. Righi explains this by supposing that 

 when light of frequency 11 is brought into a magnetic field and 

 passed a/oHi.'the lines of the field, it is split up into two sets of 

 ■ circular waves, a right-handed and a left-handed set, one of 

 which sets is accelerated and the other retarded. There are 

 now two frequencies «,, ti„, one a little higher and the other a 

 little lower than ii. But since the analyser is adjusted to ex- 

 „tinguish «, there is brightness for «j, n^. Normally, nitric 

 joxide absorbs green, and red is observed ; but when the magnetic 

 (field is set up, blue-green light is seen at the analyser ; for there 

 lare now two different kinds of light being absorbed, one of 

 higher and one of lower frequency than the normal, and what 

 lis observed is the complementary spectrum. Again, if a tube 

 Jof sodium is warmed to a point far short of that which would 

 cause it to emit visible rays, and the vapour is passed into the 

 fmagnet gap, at the moment when the magnetic field is set up 

 ithe D line becomes vi.sible in the observing spectroscope, i.e. 

 Ithe emission spectrum is obtained of a substance which is not 

 (actually emitting light. Mr. Blakesley said that no doubt the 

 analyser was used at the position of extinction for convenience 

 merely. In other positions the eye would be overwhelmed with 

 ilight. — Mr. Albert Campbell then read a paper on the magnetic 

 (fluxes in meters and other electrical instrument.s. He has 

 [recently undertaken the measurement of the magnetic fluxes and 

 (fields in certain instruments, to determine the order of magnitude 

 lof the flux density. In other cases the total flux is measured ; 

 land in the tests on meters, the power lost in the various parts of 

 (the instruments is determined. For the measurement of B, the 

 (ordinary ballistic-galvanometer method is employed, with an 

 exploring-coil. But, for alternating fluxes, two special methods 

 jare adopted, in the first of which the exploring-coil is in 

 J series with a heating-coil as.sociated with a thermopile ; 

 "in the second, a telephone is connected in series with the search- 

 Icoil and a potentiometer resistance strip. A constant current is 

 sent through the strip from the main alternate-current circuit 

 (Supplying the meter or other apparatus ; the telephone and 

 Isearch-coil therefore forms a shunt to that circuit at the strip. 

 I The search-coil is put into position in the field to be tested, and 

 Ithe strip is then adjusted to give silence in the telephone. All 

 il these methods are described in detail in the paper, and very 

 (important deductions are made, especially as regards the in- 

 I fluence of the earth's field on instruments generally assumed to 

 (be independent of the earth's H. In a few cases, diagrams are 

 'given of the fluxes in magnets, showing exactly what proportion 

 'iof the total flux is effective at the gap. Dr. S. P. Thompson 

 V suggested that as the paper was of great significance to all who 

 'were interested in the design of electric meters and other 

 (measuring instruments involving a knowledge of magnetic 

 J fluxes and their variation, an opportunity should be given for 



1a full discussion. — The President proposed votes of thanks, and 

 adjourned the discussion of Mr. Campbell's paper to the next 

 meeting on November II. 



I Paris. 



1 Academy of Sciences, October 31.— M. Wolf in the chair. 

 — Remarks on rotatory magnetic polarisation, and anomalous 

 NO. I 515, VOL. 59] 



dispersion, by M. Henri Becquerel. Remarks concerning the 

 experiments of MM. Macaluso and Corbino. A bundle of polar- 

 ised white light traverses the pierced armature of a strong electro- 

 magnet, and is analysed by a spectroscope after passing through 

 a sodium flame placed in the field. The absorption bands under 

 these conditions are seen when the current is passing to be bor- 

 dered by a series of bright dark bands, which are displaced on 

 rotating the analysing nicol. — Peculiarities relating to the innerv- 

 ation and general physiological properties of the nerves of the 

 sfhiiiitcr ani, by MXI. S. Arloing and Edouard Chantre. — ^On 

 divergent series and functions defined by a Taylor's series, by 

 .M. Le Roy. — A property of a first integral of the equations of 

 dynamics of two variables with homogeneous potential, by MM. 

 W. Ebert and J. Perchot. — On the ratio of the two specific 

 heats of gases, and its variation with temperature, by M. A. 

 Leduc. From the formulae developed in previous papers 

 the author concludes that 7, the value for the ratio 

 of the two specific heats of air, varies slightly with 

 the temperature, the ratio 70/7100 being about i '0006. 

 The variation is much more rapid with carbon dioxide, for 

 which 7(i/7ion is I '028. From the experiments of Wiillner, 

 the values of y^, are calculated for .several gases. — New ap- 

 paratus for the measurement of luminosity, by M. Onimus. The 

 apparatus described permits of the comparison of the light 

 intensities cf two days, or of one country with another. The 

 method adopted is a photographic one, the tint taken up by a 

 standard sensitised paper under fixed conditions being compared 

 with a tintometer prepared by superposing pellicles of slightly 

 tinted collodion ; the deepest tint. No. 24, being composed of 

 24 pellicles of collodion. The apparatus is extremely simple, 

 and can be used without any special knowledge of photography, 

 the ferro-prussiate paper used requiring only washing with water 

 after exposure. — Action of phenylhydrazine upon chloranilic 

 acid, by M. A. Descomps. The result of the reaction is a well- 

 crystallised substance of the composition C^Cl., Oo, 



(OH.C6H6.NH.NH0),, 

 analogous to the body obtained by JNIM. Baeyer and Kochen- 

 doerfer by the interaction of phenylhydrazine and phloroglucinol. 

 — On the presence of a soluble proteo-hydrolytic ferment in 

 mushrooms, by MM. Em. Bourquelot and H. Herissey. A 

 solution of the ferment was obtained by triturating the fungi 

 Amanita miiscaria and Clitocybe nebtilaris with sand and chloro- 

 form water, and this was allowed to act upon milk, specially 

 freed from fat. The action of the ferment is analogous to, if 

 not identical with, trypsine.— On the influence ;f temperature 

 on the determination of sex, by M. Marin Molliard. Experi- 

 ments carried out on the development of Meniirialis annua at 

 varying temperatures show-ed that heat favours, in this case, the 

 production of female individuals. — Characters of the latent life of 

 bulbs and tubers, by M. Leclerc du Sablon. — The limurites in 

 contact with the granitic rocks of the Hautes-Pyrenees, by M. A. 

 Lacroix. These rocks are characterised by the existence of a 

 violet axinite, which sometimes forms nearly the whole rock 

 mass, but is more often accompanied by pyroxene, quartz, 

 albite, and other ininerals. — Experimental study of subterranean 

 sedimentation, by M. Stanislas Meunier. — On the .secondary 

 formations of the south of the Montagne-Noire, by M. Rene 

 Nickles. — The absorption of mercury by leucocytes, by M. 

 Henri Stassano. The leucocytes of the blood of dogs, into 

 whose veins minute quantities of mercury perchloride had been 

 injected, showed, after careful separation, the presence of a 

 perceptible amount of mercury. "The experiments show clearly 

 that the leucocytes are the exclusive agents of transportation 

 and absorption of mercurial compounds in the circulation. 



GOTTINGEN. 



Royal Society of Sciences. — The Nachriahtcn (physico- 

 mathematical section), part iii. for 1S9S, contains the following 

 memoirs communicated to the Society : — 



May 14. — G. Kummell : The climatological data of Gottingen 

 for the years 1887-1896. 



March 19. — E. Wiechert : Experimental researches on the 

 velocity and magnetic deviability of the kathode-rays. 



July 9. — W. Voigt : On the light which penetrates the second 

 medium in so-called "total" reflexion. — A Hurwitz : On the 

 composition of quadratic forms of any number of variables. — 

 E. 'Timerding : The Reyeian geometry of the continua of 

 projective ground-forms. 



