Februak 



NATURE 



359 



beli ved offered a feasible solution of the problem. In this 

 machine the collectors were supposed joined to the ends of the 

 vibrating circuit, and would therefore become + and - alter- 

 nately. Inductors and brushes were to be so arranged that an 

 insulating cylinder turning between them should have many + 

 and - charges distributed alternately round its periphery. By 

 suitable adjustment these charges could be collected at the 

 proper instants so as to keep up the vibration. — The chairman, 

 Prof. Lodge, said the paper was very suggestive and full of in- 

 teresting points. The subject of electromagnetic vibrations was 

 attracting great attention in America in connection with the 

 manufacture of light. Hertz's oscillations die out too soon to 

 be satisfactory, for their duration rarely exceeds a thousandth 

 part of the interval between consecutive discharges. The theory 

 of dynamos charging condensers he considered extremely in- 

 teresting, and thought the fact that the damping factor could be 

 changed in sign must have tremendous consequences. — Dr. W. 

 E. Sumpner asked a question about a method of doubling 

 frequency of alternation recently described by Mr. Trouton, 

 in which the armature of one alternator excites the 

 fields of a similar machine. Mr. Trouton had said 

 that after once doubling the frequency it was not 

 possible to go on doing so. He (Dr. Sumpner) thought 

 that by adding other machines the frequency could be 

 still further increased, and gave a proof of the fact. In reply, 

 Prof. Fitzgerald said that adding another machine increased the 

 frequency by a given amount and did not double the preceding 

 one. Hence to increase the frequency a thousand-fold, a 

 thousand machines would be required, and on this account Mr. 

 Trouton considered it impracticable. Prof. S. P. Thompson 

 thought the paper very suggestive, and the acoustic analogies 

 very interesting. Melde's apparatus was an instance of doubling 

 or halving a frequency. On reading the title of the paper, he 

 had expected hearing of a method of maintaining electromag- 

 netic vibrations by giving occasional impulses in some such way 

 as that in which a tuning-fork could be kept vibrating by allow- 

 ing the hammer of a trembling bell to knock against it. There 

 was another method of intensifying electric oscillations which he 

 had only seen mentioned in a patent specification by Sir W. 

 Siemens, who suggested using a series dynamo with a telegraph 

 cable to augment the signalling currents. On the subject of 

 ironless dynamos he (Prof. Thompson) desired further informa- 

 tion. Some years ago he had made calculations and found the 

 speed at which they would require to run was so enormous as to 

 be beyond the range of engineering possibility. Mr. C. V. 

 Boys, referring to the author's suggestion of using an electric 

 spark with alternate paths to maintain vibration, said that he 

 had tried whether an oscillatory spark was displaced by a mag- 

 netic field, but the displacement, even when photographed by a 

 revolving mirror, was barely appreciable. Prof. Perry asked for 

 an explanation of the term "skin-deep magnetism." He was 

 not previously aware that Sir W. Siemens had described a 

 method of improving cable signalling by using a series dynamo. 

 He himself had patented a somewhat similar arrangement. He 

 had also made a dynamo without iron, but had not got it to 

 work. In reply to Prof. Perry the author of the paper said that 

 in electromagnetic vibrations the magnetic force alternates so 

 rapidly that it could not penetrate far into the field magnet of a 

 dynamo before it is reversed ; hence the magnetism would only 

 be skin-deep. Dr. Burton suggested that a commutator with 

 many segments, something like that used by Mr. Gordon in his 

 researches on specific inductive capacity, might possibly be em- 

 ployed for producing high frequencies. — .A communication on 

 supplementary colours, by Prof. S. P. Thompson, F. R.S., was 

 postponed. 



Entomological Society, January 27. — The fifty-ninth 

 annual meeting, which had been adjourned from the 20th insL 

 on account of the death of H. R.H. the Duke of Clarence. — 

 Mr. F. DuCane Godman, F. R.S., President, in the chair. — An 

 abstract of the Treasurer's accounts, showing a good balance in 

 the Society's favour, having been read by one of the Auditors, 

 the Secretary, Mr. H. Goss, read the Report of the C^ouncil. 

 It was then announced that the following gentlemen had been 

 elected as Officers and Council for 1892 :— President : Mr. 

 Frederick DuCane Godman, F. R. S. Treasurer : Mr. Robert 

 McLachlan, F. R.S. Secretaries: Mr. Herbert Goss and the 

 Rev, Canon Fowler. Librarian : Mr. George C. Champion. 

 And as other Members of the Council : Mr. C. G. Barrett, 

 Mr. Herbert Druce, Captain Henry J. Elwes, Prof. Raphael 

 xMeldola, F.R.S., Mr. Edward B. Poulton, F.R.S., Dr. David 



NO. II 63, VOL. 45] 



Sharp, F.R.S., Colonel Charles Swinhoe, and the Right Hon. 

 Lord Walsingham, F.R.S. It was also announced that the 

 President would appoint Captain Elwes, Dr. Sharp, and Lord 

 Walsingham, Vice-Presidents for the session 1892-93 — The 

 President then delivered an address. After alluding to the vast 

 number of species of insects, and to the recent calculations of 

 Dr. Sharp and Lord Walsingham as to the probable number of 

 them as yet undescribed, he referred to the difficulty experienced 

 in preparing a monograph of the fauna of even a comparatively 

 small part of the world, e.g. Mexico and Central America, and 

 certain small islands in the West Indian Archipelago, upon 

 which he, with a large number of competent assistants, had been 

 engaged for many years. The examination of the collections 

 recently made in St. Vincent, alone, had obliged him to search 

 the whole of Europe and North America for specialists ; and 

 similar collections from Grenada were still untouched in con- 

 sequence of the number of workers being unequal to the de- 

 mands upon their time. He observed that the extent of the 

 subject of entomology was so vast that nothing but a systematic 

 and continuous effort to amass collections, work them out, and 

 preserve them, could place us in a position to proceed safely 

 with the larger questions which followed the initial step of 

 naming species : and it would only be by the steady effort of 

 our Museum officials, not only to work at the subject them- 

 selves, but to enlist the aid of every available outside worker, 

 that substantial progress could be made. The President con- 

 cluded by referring to the losses by death during the year of 

 several Fellows of the Society and other entomologists, special 

 mention being made of M. Andre, the Duke of Devonshire, 

 Mr. F. Grut, Mr. E. W. Janson, Prof. Felipe Poey, Sir 

 William Macleay, Mr. H. Edwards, Mr. Robert Giilo, and 

 Dr. J. M, J. Af Tengstrom. 



Geological Society, January 27.— Dr. W, T. Blanford, 

 F.R.S., Vice-President, in the chair. — The following communi- 

 cations were read : — On the hornblende-schists, gneisses, and 

 other crystalline rocks of Sark, by the Rev. Edwin Hill and 

 Prof. T. G. Bonney, F.R.S. The authors refer to Mr. Hill's 

 paper, published in 1887, for a general description of the island. 

 They were led to examine Sark again in the hope that its rocks 

 might afford some clue to the genesis of the hornblende-schist 

 of the Lizard. They describe the structure, macroscopic and 

 microscopic, of the various foliated rocks. These are : — {a) 

 The basement gneiss, a slightly foliated, somewhat granitoid 

 rock, probably of igneous origin, but with some abnormal en- 

 vironment, and possibly intrusive into, instead of older than the 

 rock which succeeds it. {b) The hornblende-schists, almost 

 identical with those of the Lizard, but in one case yet more 

 distinctly banded, {c) Banded gneisses, sometimes rather fine- 

 grained, variably banded ; quartzofelspalhic layers alternating 

 with those rich in biotite or occasionally hornblende. Some of 

 these gneisses resemble the "granulitic group" of the Lizard ; 

 others recall certain of the less coarse, well-banded gneisses of 

 Scotland, e.g. south of Aberdeen. Sometimes they are much 

 j "gnarled" by subsequent earth-movements, by which, however, 

 1 as a rule, the crystalline rocks of the island do not appear to 

 I have been very seriously affected, {d) A very remarkable group 

 ! of local occurrence which exhibits great variety. In some places 

 i large masses of a dark green hornblende-rock are broken up and 

 I traversed by a pale red vein-granite or aplite. The former rock 

 is drawn out into irregular lenticles, elongated lumps, and finally 

 streaks, and has been melted down locally into the aplite. This 

 I then becomes a well-banded biotite gneiss, which macroscopically 

 and microscopically agrees with types which are common among 

 the Archaean rocks. Sark therefore presents an example of the 

 genesis of such a gneiss, and the authors are of opinion that 

 probably all the above-named rocks are of igneous origin, but 

 became solid ultimately under somewhat abnormal conditions, 

 to which the peculiar structures (which distinguish them from 

 ordinary igneous rocks) are due. They attribute the banding to 

 the effect of fluxional movements, anterior to final consolidation, 

 in a mass to some extent heterogeneous. This hypothesis they 

 consider may be applied to all gneisses or schists which exhibit 

 similar structures — that is, to a considerable number (but by no 

 means all) of the Archaean rocks. The second part of the paper 

 consists of notes on some of the dykes and obviously intrusive 

 igneous rocks of the island. Among these are four (new) 

 dykes of " mica-trap," one of which exhibits a very remarkable 

 "pisolitic" structure. The variety of picrite described by Prof. 

 Bonney in 1889 (from a boulder in Port du Moulin) has also 

 been discovered in situ. The reading of this paper was followed 



