142 



NA TURE 



[December 7, 1893 



dynamo itself be shielded, this did not prevent the currents in 

 the leads producing magnetic disturbances. This was very im- 

 portant in ships. By using an alternator vi'ith resolving fields 

 all disturbances could be avoided. Dr. C. V. Burton inquired 

 whether by considering the hydrodynamical analogue of a porous 

 material the case of perforated shells could be elucidated? Mr. 

 A. P. Trotter wished to know if the homogeneity of the shield 

 was of much consequence? At Oxford it had been found 

 that a screen of four inches of scrap-iron was better than boiler- 

 plate. Mr. Blakesley asked if the effect of moving a magnet 

 sideways in a sphere had been observed. He thought the mathe- 

 niatics developed in the paper would be useful in working out 

 the magnetic theory of the earth. Prof. S. P. Thompson 

 thought that taking the permeability as constant would not be 

 quite correct, for ^x. was a function of the magnetisation. Hence 

 in the cases considered the outer shell would be the more per- 

 meable. In his reply, the President said scrap-iron in contact 

 was not like clear space, for there were comparatively free paths 

 lor the induction at the points of contact. As regards the 

 shielding of the dynamo at Greenwich, Mr. Christie had written 

 to say that the credit was due to the makers of the machine and 

 shields, Messrs. Johnson and Phillips. — Prof. G. M. Minchin 

 read a paper on the action of electromagnetic radiation on films 

 containing metallic powders. After noticing the resemblance of 

 the phenomena exhibited by tubes containing metallic filings 

 shown by Mr. Croft, on October 27, to those of photoelectric 

 impulsion cells, he repeated some of the experiments with filings, 

 and found the same effects when the filings were of ordinary 

 fineness. He also noticed that the experiments did not succeed 

 either when the filings were coarse or very fine. Coarse ones 

 always conducted, whilst very fine filings or powders acting as 

 insulators, except when strongly compressed. To establish a 

 closer connection with the impulsion cells he tried films of gela- 

 tine and collodion containing metallic powders. Directions for 

 preparing the films are given in the paper. On inserting such 

 a film in circuit with a battery, key, and galvanometer, it acts 

 as an insulator. To render a small portion conducting, the 

 electrodes on the surface of the film are brought very close to- 

 gether, and one of the wires touched with an electrified body 

 (an electric gas-lighter was often used). This caused a current 

 to pass. The electrodes may then be separated a little further, 

 and the process repeated until any desired portion is rendered 

 conducting. The peculiarity of such a film is that if the circuit 

 be broken at the film, the film becomes an insulator ; whereas 

 breaking the circuit at any other point leaves the film conducting. 

 The action of the sparks or charges on the conductivity of the 

 films is attributed to the influence of electric surgings in the 

 wires by the electric discharges. The President read a written 

 communication from Pr.>f. O. J. Lodge, in which the writer 

 suggested that the phenomena of the films, and also of Lord 

 Rayleigh's water-jet experiment (in which water-drops are 

 caused to coalesce by the presence of an electrified body), were 

 due to the range of molecular attraction being increased by 

 electric polarisaiion. Mr. Blakesley said he had tried Mr. 

 Croft's experiments, and found that conductivity could be 

 established in a tube of filings whilst the circuit was unclosed. 

 Breaking the circuit of a transformer or electromagnet would 

 produce conductivity ; hence he concluded that electric surg- 

 ings were not essential. Another curious experiment was to 

 put the discharging knobs of an electric machine on a i hoto- 

 graphic plate at a distance of a few inches. On turning the 

 machine a small spark travels slowly along the plate from the 

 negative to the positive knob. On reversing the polarity of the 

 machine the spark travels back along the same path, but if the 

 polarhy remains unchanged a second spark usually travels along 

 a different path. Prof. C. V. Boys asked Prof. Minchin 

 whether the films themselves, or the contacts between the elec- 

 trode and film is made conducting by the sparks ? Prof. S. P. 

 Thompson wished to know if ordinary photographic dry-plates 

 would serve the purpose ? Mr. Evershed inquired whether the 

 metal used as electrode made any difference ? Prof. Minchin, in 

 his reply, maintained that the phenomena were due to electric 

 impulses. He had not tried photographic plates, and had always 

 used platinum for his electrodes. 



Chemical Society, November 16. — Dr. Armstrong, Presi- 

 dent, in the chair.— A letter has been addressed to Prof. 

 Mendeleef, congratulating the Russian Chemical Society on the 

 celebration of its twenty-fifth anniversary. The following papers 

 were read : — The normal butylic, heptylic, and octylic ethereal 

 salts of active glyceric acid, by P. Frankland and J. 



NO. 1258, VOL. 49] 



MacGregor. The authors have determined the rotatory powers 

 of the homologous series of ethereal salts of active glyceric acid 

 up to octylic glycerate ; the molecular rotations .of the normal 

 and secondary butylic salts are greater than those of any others 

 of the series. This kind of result has been predicted by Guye. 

 — The ethereal salts of diacetylglyceric acid in relation to the 

 connection between optical activity and chemical constitution, 

 by P. Frankland and J. MacGregor. The authors have pre- 

 pared the methylic, ethylic, propylic, isopropylic, and isobutylic 

 salts of active diacetylglyceric acid. In the case of the first two 

 of these salts, two of the atomic groups attached to the assy- 

 metric carbon atom are of equal mass ; according to Guye's 

 theory, these should be almost, or quite, optically inactive. This, 

 the authors find, is not the case, and they therefore again urge 

 that the qualitative nature of the groups attached to the assy- 

 metric carbon atom must be considered, as well as their masses. 

 — The oxidation of paratoluidine, by A. G. Green. The red 

 base obtained by Barsilowsky by oxidising paratoluidine with 

 ferrocyanide is a diparatolylimide of the constitution 



MeC 



\ 



.C: (NC-H-)-CHx 

 CH-C : (NC-Hy)^ 



>CNH„ 



On reduction it yields a stable leuco-base. — The action of benzoic 

 chloride on urine in presence of alkali. Formation of benzoic 

 derivatives of urochrome, by J. L. W. Thudichum. By the 

 action of benzoic chloride on alkaline urine, a mixture of benzoic 

 derivatives of urochrome is deposited. — The combination of 

 hydrocarbons with picric acid and other nitro compounds, by 

 \V. A. Tilden and M. O. Forster. Picric acid combines with 

 terpene, giving a compound which forms a peculiar potassium 

 salt, yields picramide and boineol when treated with alcoholic 

 ammonia, and gives borneol when treated with aqueous alkalis. 

 — The formation of pyrrol derivatives from aconitic acid, by S. 

 Ruhemann and F. E. Allhusen. — The conversion of a hydrin- 

 donoxime intohydrocarbostyril, by F. S. Kipping, a-hydrindon- 

 oxime yields hydrocarbostyril when treated with phosphorus pen- 

 tachloride. — The constitution of lapachol and its derivatives. II. 

 The azines of the lapachol group, by S. C. Hooker. The author 

 describes methyllapazire, melhyllapeurhodone, methylhydroxy- 

 lapeurhodone, and several of their halogen derivatives. 



Geological Society, November 22. — W. H. Hudleston, 

 F. R. S., President, in the chair. — The following communications 

 were read : — The basic eruptive rocks of Gran, by Prof. W. C. 

 Brogger. In previous communications the author has main- 

 tained that the different masses of eruptive rock which occur 

 within the sunken tract of country lying between Lake Mjosen 

 and the Langesundsfjord are genetically connected, and have 

 succeeded each other in regular order. The oldest rocks are 

 the most basic, the youngest (except the unimportant dykes of 

 diabase) are the most acid, and between the two extremes he 

 has found a continuous series. He is now preparing a detailed 

 monograph on this series of eruptive rocks, and in the present 

 communication he gave an account of the results of his work on 

 the oldest members. Several bosses of basic plutonic rock, now 

 forming a series of dome-shaped hills, lie along a northand- 

 south fissure line. The most northerly is that of Brandberget 

 in the parish of Gran, about 50 or 60 kilometres north-north- 

 west of Christiania, and the most southerly occurs at Dignaes on 

 Lake Tyrifjord, about 35 kilometres west-north-west of the 

 same town. The prevailing rock in these bosses is a medium 

 or coarse-grained olivine-gabbro-diabase ; but pyroxenites, 

 hornblendites, camptonites, labrador-porphyrites, and augite- 

 diorites also occur. - Analyses of the typical rocks from three 

 localities on the north and south line were given, and the con- 

 clusion was reached that the average basicity of the rocks form- 

 ing different bosses decreases from north to south. Thecontact- 

 metamorphi-m was referred to ; and the presence of hypersthene 

 in the altered Ogygia-%\\d\&i,, coupled with its absence from the 

 same shales where they have been affected by quartz-syenite, 

 led the author to the conclusion that the chemical nature of the 

 intrusive rock does, in certain cases, produce an influence on 

 the character of the metamorphism. Innumerable dykes and 

 sheets of camptonite and bostonite are associated with the 

 above-mentioned plutonic bosses. These are regarded by the 

 author as having been produced by differentiation from a 

 magma having the composition of the average olivine- 

 gabbro-diabase. Analyses were given, and it was proved 

 that a mixture of nine parts of the average camptonite 

 and two of the average bostonite would produce a magma 



