214 



NATURE 



[June 30, 1892 



SCIENTIFIC SERIALS. 



The numbers of the Journal of Botany for May and June 

 appeal almost entirely to students of systematic and descriptive 

 botany : — Mr. F. J. Hanbury continues his notes on Hieracia 

 new to Britain, in the course of which he describes three 

 species altogether new. — Mr. Geo. Massee contributes diagnoses 

 of a number of new species of Fungi from St. Vincent, illus- 

 trated by three coloured plates. — Mr. E. G. Baker continues 

 his Synopsis of genera and species of Malvern; Rev. Moyle 

 Rogers his essay at a key to British Rubi ; and Mr. W. A. 

 Clarke his first records of British flowering plants. 



In the Botanical Gazette for May are two original papers of 

 interest : — On the archegone and apical growth of the stem in 

 Tsuga canadensis and Pimis sylvestris, by D. M. Mottier. On 

 the first point the author agrees very nearly with the account 

 by Strasburger ; on the second point he is unable to say that 

 there is a single cell at the apex of the stem, unless in the 

 young plant, and even then not with absolute certainty. — Ger- 

 mination of the teleutospores of Ravenalia cassiacola, by B. M. 

 Duggar. 



SOCIETIES AND ACADEMIES. 



London. 

 Physical Society, June lo. — Mr. Walter Baily, Vice- 

 President, in the chair. — Dr. Gladstone read a paper on some 

 points connected with the electromotive force of secondary 

 batteries, by himself and Mr. W. Hibbert. The communi- 

 cation includes replies to certain questions raised by M. Darrieus 

 in a paper read before the Societe Internationale des Electriciens 

 on May 4, 1892 ; and to the views expressed by Prof. Arm- 

 strong and Mr. Robertson in the discussion on a paper by 

 the present authors read before the Institution of Electrical 

 Engineers, on May 12 and 19. It also contains an account of 

 their recent experiments on the subject. M. Darrieus agrees 

 with Prof. Armstrong and Mr. Robertson that the large E. M. F. 

 immediately after charge is due to persulphuric acid, and 

 opposes the ordinary theory that the ultimate product of dis- 

 charge is lead sulphate at both plates, so far as the positive 

 plate is concerned. The authors attribute the finding of large 

 quantities of lead oxide by M. Darrieus to difficulties in analysis, 

 for it is not easy to imagine that oxide of lead could remain as 

 such in presence of sulphuric acid. They have also shown that 

 the changes of E. M.F. during charge and discharge coincide 

 fairly well with those obtained by putting Pb and PbOg plates 

 in different strengths of acid, and conclude "that the changes 

 ofE.M. F. . . . depend on the strength of the acid that is against 

 the working surfaces of the plates." Prof. Armstrong and Mr. 

 Robertson disagree with the authors' views, and suppose that 

 the sulphuric acid used was contaminated with soluble 

 peroxides ; and they also believe that H2SO4 itself takes part in 

 the reactions. As regards the first objection, the authors see no , 

 reason why the traces of soluble peroxide (if any) on the plates 

 should always vary in amount with the strength of the fresh acid 

 in which the plates were dipped. The second point they leave 

 an open question. In reply to the criticism on the summation of 

 the two curves obtained respectively with two lead plates and 

 two lead peroxide plates in acids of different strengths, they 

 point out that the resulting curve coincides both in shape and 

 magnitude with that determined when a Pb and a PbOg plate 

 were placed in different strengths of acid. Whilst admitting the 

 possibility of the lead supports having some influence on the 

 result, they cannot conceive that such large and uniform 

 differences as those given in their paper can be due to accidental 

 operations of local action. To show that the increase of E.M.F. 

 does not depend on the presence or absence of persulphuric 

 acid, the authors have tested the E.M.F. of a Pb and a PbOg 

 plate, free from soluble oxides, in sulphuric acid of 15 per cent, 

 strength, a porous diaphragm being between the plates. The 

 E.M.F. was I '945 volts. After adding I per cent, of per- 

 sulphate of potassium to the liquid surrounding the PbOj plate, 

 the E.M.F. was unaltered ; whilst putting the Pb plate in the 

 same liquid only reduced the E.M.F. to I "934. Experiments 

 had also been made on cells with phosphoric acid of different 

 strengths, instead of sulphuric acid. Changing the density from 

 I -05 to I '5, raised the E.M.F. o'i76 volt, whilst calculations 

 from Lord Kelvin's law gave o'i7i volt. In this case they con- 

 sider that no acid analogous to peraulphuric acid could be 



present. They also find that the effects of charging and repose 

 on the E.M.F. of phosphoric acid cells are quite analogous to 

 those obtained with sulphuric acid. The researches are being 

 extended chiefly on the thermochemical side. Prof. Ayrton 

 thought there was no question that the strength of acid had 

 much to do with the changes of E.M.F. The point at issue, he 

 considered, was whether the changes were direct effects of the 

 strength of acid, or due to secondary actions brought about by 

 alterations in strength. Mr. E. W. Smith said Mr. Robertson 

 and himself were repeating the author's experiments with 

 two PbO._j plates without any grid. They had obtained results 

 analogous to those mentioned in the paper, but the true 

 explanation of the effects was still to seek. Mr. W. Hibbert 

 contended that the soluble oxides referred to by Prof. Arm- 

 strong and Mr. Robertson were not present in their experiments. 

 j They had also proved that changes in acid strength altered the 

 I E.M.F., whilst presence of persulphuric acid did not. Dr. 

 j Gladstone, in reply, said they also were making experiments 

 ' without grids, but had not made sufficient progress to discuss 

 them at present. Mr. Hibbert and himself believed the effects 

 of local action inconsiderable, whilst Messrs. Armstrong and 

 Robertson thought them very important. He hoped that ere 

 long the points would be settled conclusively. — A paper on 

 workshop ballistic and other shielded galvanometers, by Prof. 

 W. E. Ayrton, F.R.S., and Mr. T. Mather, was read by 

 Prof. Ayrton. The galvanometers described were of the type 

 having movable coils and fixed magnets, the advantages of 

 which are well known. In designing the ballistic instruments, 

 their aim had been to obtain sensibility and portability, com- 

 bined with being screened from external influences, for it was 

 often desirable to measure the magnetic fluxes and fields in 

 dynamos by apparatus near the machines. One of the improve- 

 ments adopted was the narrow coil described in a paper " On 

 the Shape of Movable Coils, &c.," read before the Society in 

 1890. Such coils are particularly advantageous for ballistic 

 instruments, for not only can greater swings be obtained by the 

 discharge of a given quantity of electricity through such a coil 

 than with ordinary shaped coils when the periodic limes are the 

 same, but even when the same control is used, the same length 

 of wire in the coil, and suspended in the same field, the narrow 

 coil is more sensitive to discharges than coils of any other shape. 

 Another improvement was the use of phosphor bronze strip for 

 the suspensions instead of round wire. For a given tensile 

 strength, both the control and the subpermanent set could be 

 diminished by using strip. In February 1888 the authors made 

 a d'Arsonval of the ordinary type as a ballistic instrument, and 

 found that although it was suitable for comparing condensers, 

 yet for induction measurements the damping was excessive 

 unless the resistance in the circuit was very large. This greatly 

 reduced the sensitiveness. In 1890 they tried one of Carpentier's 

 milliamperemeters as a ballistic instrument, but found it in- 

 sensitive. A narrow coil instrument made in the same year 

 was found to be sensitive for currents ; but as the coil was wound 

 on copper to get damping, it was not suitable for ballistic work. 

 In January 1892 a somewhat similar instrument was constructed 

 for ballistic purposes, and was found very sensitive and con- 

 venient. Although the coil had only a resistance of 13 ohms, 

 one microcoulomb gave a swing of 170 divisions on a scale 

 2000 divisions distant, the periodic time being 27 seconds. 

 The instrument could be used near electromagnets or dynamos, 

 and was so sensitive that for ordinary induction measurements 

 very large resistances can be put in series with it, thus reducing 

 the damping to a very small amount. On the other hand, the 

 coil could be brought to rest immediately by a short circuit 

 key. It had the further advantage that it was not necessary to 

 redetermine its constant every time it was used. The chief 

 disadvantage of such instruments was the variable damping 

 on closed circuits of different resistances. This could, however, 

 be overcome by arranging shunts and resistances so that the 

 external resistance between the galvanometer terminals was the 

 same for all sensibilities. A portable ballistic instrument, 

 intended for workshop use, was next descrilied. This had a 

 narrow coil and a pointer moving over a dial whose whole 

 circumference was divided into 200 parts. The instrument had 

 been designed to give a complete revolution for a reversal of a 

 flux of two million C.G. S. lines, but the pointer could turn 

 through two or more revolutions. To test strong fields a test coil 

 with a total area of 10,000 square centimetres is used, and has a 

 trigger arrangement for suddenly twisting it through two right 

 angles. The instrument then reads off directly the strength of 



NO. I 183, VOL. 46] 



