228 



NA TURE 



[Al'RIL 2 2, 1909 



the pendulum may be made to ascend or descend with a 

 given acceleration ; in the former case the time of swing 

 is decreased, in the latter increased, and the two times are 

 determined from the strip records of the upwai'd and 

 downward motions. In the example given by the author 

 the agreement between the observed and calculated ratio 

 of the times of swing is within one part in one thousand. 



The Journal de Physique for March contains a descrip- 

 tion of the apparatus for radio-active measurements by the 

 electroscope method exhibited by Messrs. C. Cheneveau 

 and A. Laborde at a recent meeting of the Soci^t^ 

 fran^aise de Physique. The electroscope is of the type 

 introduced by the late Prof. P. Curie, the leaf of aluminium 

 being supported by a plate rising from the base of the 

 instrument, where it is insulated by passing through a 

 plug of "ambroid." To its lower end a short or a long 

 rod may be attached. Radio-active solids are placed in 

 a shallow cylinder under the electroscope into which a 

 short rod connected with the leaf projects. Gases are 

 tested in a longer cylinder, into which a long rod projects. 

 The aluminium leaf is observed through a microscope with 

 a scale in the eye-piece, one division of which corresponds 

 to 0-4 volt. The normal rate of lealc of the instrument 

 is I volt in twelve minutes, and the minimum for a 

 measurement i volt a minute. The lowest rate of pro- 

 duction of radium emanation measurable with the larger 

 cylinder is 0-002 milligram per minute. The authors hope 

 that the simplicity of the apparatus will lead to its extensive 

 use. 



Messrs. J. W. Gray and Son, the well-Vcnown lightning- 

 conductor experts, of 91 Leadenhall Street, have sent us 

 a pamphlet, from the pen of their senior partner, Mr. 

 Alfred Hands, entitled " Lightning and the Churches." 

 The author estimates that not more than 25 per cent, or 

 30 per cent, of the ecclesiastical buildings in this country 

 are provided with lightning conductors. Statistics which 

 he has collected show that about twenty-four such build- 

 ings are damaged every year by lightning, and that of 

 these about three are fitted with conductors which have 

 failed to afford protection. Failure, he considers, may be 

 due to original faults of construction or arrangement, to 

 decay of important parts, or to alterations made in some 

 of the metallic portions of the building after the conductor 

 had been fixed. It is urged that the system of protection 

 should be designed by an expert to suit each particular 

 case, and should be inspected and tested at least once in 

 every three years. The book contains many interesting 

 photographs illustrating the destructive effects of lightning, 

 and concludes with a list of 244 cathedrals, churches, and 

 chapels which have been damaged by lightning during the 

 last ten years. 



The principal features of the Bulletin de la Classe des 

 Sciences (1908, No. 12) of the Royal Academy of Belgium 

 are a paper by P. Bruylants on the derivatives of tri- 

 methylene and a paper by J. Fraipont on the okapi and 

 its affinities with living and with e.xtinct giraffes. The 

 former paper, extending over eighty-four pages, contains 

 a description of a wide range of compounds containing the 



group I ~>CHX, the boiling points and densities of 



CH„/ 

 which are contrasted with those of the isomeric allyl com- 

 pounds CH2 = CH.CHjX, and of the isopropyl compounds 



/-.rj'^CHX; the trimethylene compounds usually have a 



higher boiling point and a higher density than the corre- 

 sponding allyl and propyl compounds. The latter paper is 



NO. 2060, VOL. 80] 



illustrated by an excellent picture in colours of the Okapia 

 johnsloni, a map showing its distribution in the Congo 

 basin, and a series of six comparative photographs of the 

 skull of the okapi and related species. 



Attention has been directed in these columns to 

 observations by Noyes which indicated that the mobility 

 of the hydrogen ion in hydrochloric and in nitric acids 

 continued to decrease at dilutions considerably greater 

 than those at which other ions exhibit constant mobilities. 

 A recent paper by Chittock in the Proceedings of the 

 Cambridge Philosophical Society records a number of 

 observations in which the same experimental result was 

 obtained, namely, an increase in the migration value of 

 hydrogen in hydrogen chloride from the normal value 

 0167 to 0-275 in very dilute solutions. The e.xplanation 

 given is, however, of a much simpler character, the 

 suggestion being .made that the decreased mobility of the 

 hydrogen ion is due to its association with traces of 

 ammonia present as impurities in the water, whereby the 

 hydrochloric acid is converted into ammonium chloride. 

 A similar conclusion had already been reached by 

 Whetham and Paine from observations of the conductivity 

 and migration velocities of dilute solutions of sulphuric 

 acid. It should not be difiicult, e.g. by distilling from 

 phosphoric acid, to prepare water practically free from 

 ammonia and basic impurities, and it would be of interest 

 to know whether such samples of water would give rise 

 to abnormalities similar to those described above. 



Messrs. Witherby and Co. have in preparation a work 

 on the "Birds of Kent," by Dr. Norman F. Ticehurst, 

 who has for many years been well known among ornitho- 

 logists as a close observer of the avifauna of the county. 

 The work will be published by subscription, and only a 

 limited edition will be issued. 



A SPECIAL meeting of the council ot the Iron and Steel 

 Institute was held on Tuesday, April 20, under the presi- 

 dency of Sir Hugh Bell, Bart., to consider the situation 

 created by the resignation of the president-elect, Sir W. 

 Thomas Lewis, Bart. A resolution of regret that Sir 

 \V. Thomas Lewis had found himself unavoidably pre- 

 cluded from assuming the office to which he had been 

 elected was passed, and at the unanimous desire of those 

 present Sir Hugh Bell consented to retain the presidency 

 for a further term of twelve months. In that capacity he 

 will, therefore, take the chair at the annual meeting and 

 at the dinner on May 13 and 14 respectively. 



OUR ASTRONOMICAL COLUMN. 



Halley's Comet. — Science Progress for the current 

 quarter (No. 12, April, p. 543) contains an interesting 

 article by Mr. Cronimelin, who reviews the past history 

 of Halley's comet and discusses the probable time of the 

 approaching perihelion passage. In the retrospect Mr. 

 Crommelin directs attention to the fact that a fifteen- 

 months' variation of the period caused Halley to hesitate 

 before accepting the conclusions regarding the object's 

 periodicity ; it is now known that the planetary perturba- 

 tions may cause a five-year variation, from seventy-four 

 to seventy-nine years. 



The identifications of returns are now carried back so 

 far as 240 B.C., although there is no certain identification 

 of Halley's with any observed comet until 12 B.C. ; its 

 appearance at that return is very fully described in the 

 Chinese annals. Mr. Crommelin regards it as certain 

 that the comet will be re-discovered as soon as the region 

 of Orion, where it now is, becomes observable in the 

 autumn of the present year. January or February, 1910, 

 should find it visible in small telescopesj or even to the 

 naked eye. 



