574 



NA TURE 



i[OCTOBKR 8, 1908 



approximation to the actual azimuths before the height 

 of the horizon has been measured. 



Now, while the summer solstice sun thus rises in 

 different azimuths with different heights of the 

 liorizon, its position in the heavens, that is, its declin- 

 ation, is unchanged. It is clear, then, that we cannot, 

 by our azimuth measures alone, obtain the true posi- 

 tion of the sun in the heavens, that is, in the celestial 

 sphere. The same remark also applies to every star 

 which rises and sets in the latitude of Britain. In 

 addition to the azimuth of the rising or setting place, 

 •we must also take the height of the horizon into 

 account. When we do this, the determination of 

 the true position -in the heavens, whether of sun or 

 star — the declination — is easy. 



As I shall show in the sequel, we have now the 

 means, as the result of astronomical calculations, of 

 determining the dates at which the sun or a star 

 occupied declinations in times past different from 

 those they occupy at present. All the archaeologist 

 has to do is to consult certain tables in which the 

 sun's declination at the solstice and the varying de- 

 clinations of the stars are shown for the past six 

 thousand years. This is enough for the purpose the 

 archjeologist has in view. 



Norman Lockyer. 



THE GROWTH AND SHRINKING OF 



GLACIERS.'' 



'pHE interesting publications referred to below show 



^ that the study of the fluctuations of glaciers is 

 making good progress. Those of the Swiss Alps have 

 been watched systematically for nearly thirty years, 

 and similar work is now being carried on, not only in 

 all parts of that chain, but also in the Pyrenees, Scan- 

 dinavia, Bokhara, the Altai, the Tian Shan, and the 

 North American chains, and has been started in the 

 Himalayas. In the European Alps a general retreat 

 of the glaciers began about 1S61. At first rapid, it 

 slackened after a time, but, though here and there a 

 glacier has slightly retraced its steps and an advance 

 became more general towards the end of the last 

 century, the majority are still either slowly shrinking 

 or at best stationary. In the French Alps, we learn, 

 sundry small glaciers have quite melted away during 

 the last few years. It is to be hoped that these places 

 will be carefully watched in order to ascertain more 

 precisely the conditions (temperature, precipitation, &c.) 

 under which the formation of a glacier becomes pos- 

 sible. That, as I pointed out in 1S94 (see " Ice 

 Work," part iii., ch. i.), would enable us to estimate 

 the mean temperature in certain localities during the 

 Glacial epoch, and thus to obtain one firmer footing 

 in that most slippery subject. This shrinkage of the 

 world's ice mantle, we may add, appears to char- 

 acterise all the countries observed, for only in Scan- 

 dinavia, and perhaps at Mount St. Elias, are glaciers 

 beginning to advance in notable numbers. 



Prof. Forel contributes to the special report on the 

 Swiss glaciers a valuable discussion on the relations 

 of their changes to the meteorology of the region, 

 founded on observations which have been taken con- 

 tinuously at Geneva for the last eighty years. The 

 advance or retreat of an ice-stream depends mainly on 

 two factors : the annual snowfall and the general tem- 

 perature, the one chiefly affecting its upper part, the 

 other its lower. The effects, especially of the former, 

 obviously cannot be immediate, and a glacier may con- 



'^ " Les Variations pi^riodiques des Glaciers." xii'"^ Rapport, 1906, de la 

 Commission internation.<ile des Glaciers. Resume' par F. A. Forel. Arck. 

 licsSc!. Phys, et Nat. Quatr. Fir., t. xxv. , pp. 577-587. 



" Les Variations piriodiques des Glaciers des Alpes Suisses." By F. A. 

 Forel, E. Muret, P. L. Mercanton and E. Argand. 2S"" Rapport, 1907. 

 E.\trait de TAnnuaire du S.A.C., xliii™= annee. Pp. 302-331. 



NO. 2032, VOL. 78] 



tinue its advance when the conditions are adverse, or 

 vice versa. As forty-three years elapsed before the relics 

 of members of Dr. Hamel's party, who perished in a 

 crevasse on the .\ncien Passage, were discovered on the 

 Glacier des Bossons, after travelling about five and a 

 half miles, we must expect changes and their results to 

 be separated by an interval, depending on the length, 

 slope, and other characters of an ice-stream. It is 

 perhaps too soon to generalise from Prof. Forel's dis- 

 cussion of the Geneva observations, and the distance 

 of that observatory from the higher parts of the chain 

 will always be a drawback ; but the results are already 

 suggestive, and his method of smoothing off the irre- 

 gularities of individual years, by taking the mean of 

 the decade which they close, enables us to form a 

 better estimate of the real climatal changes. Time 

 will render the work of the professor, his coadjutors, 

 and all members of the International Commission in- \ 

 cieasingly valuable; for this is one of the cases where 

 one generation must plant the tree and another gather 

 tha fruit. 



T. G. BONNEY. 



IXTERN.4TI0NAL CONFERENCE ON ELEC- 

 TRICAL UNITS AND STANDARDS. 

 DY invitation of the British Government an Inter- 

 -'-' national Conference on Electrical Units and 

 Standards will be held in London at the rooms of 

 the Royal Society during this month. Eighteen 

 countries are sending delegates to the conference ; the 

 names are given below. 



The first meeting of the conference will be held 

 on Monday, October 12, at 11.30, when the delegates 

 will be received by the President of the Board of 

 Trade; in the evening there will be a reception by the 

 Royal Society. The meetings of the conference are 

 expected to last until October 22, but this date is not 

 fi-xed, as it will entirely depend on the progress made 

 with the work at the conference. 



The main object of the conference is to obtain 

 international agreement on the three electrical units, 

 the ohm, the ampere, and the volt, so that the 

 realisation of these units in all the countries of the 

 world shall be as near as possible identical. The best 

 method of setting up the mercury ohm, the silver 

 voltameter, and cadmium cell will be considered, and 

 it is hoped that detailed specifications may be issued 

 with the authority of the conference. 



The delegates, will be entertained at an official 

 banquet, and will lunch with the Lord Mayor; they 

 will also make an excursion to Cambridge on the 

 invitation of Trinity College, and pay a visit to the 

 Cavendish Laboratory. The Board of Trade Govern- 

 ment Standards Laboratory will be open to inspection 

 by the delegates, and the National Physical Labora- 

 torv at Teddington will be visited. The delegates 

 will also dine at the Franco-British Exhibition with 

 the " Dynamicables," and are invited to the annual 

 dinner of the Institution of Electrical Engineers. 



List of Delegates. 



.America (Viiitcd States).- — Dr. Henry S. Carhart, pro- 

 fessor of physics at the University of Michigan : Dr. 

 S. \V. Stratton, director, Bureau of Standards, Wash- 

 ington ; Dr. E. B. Rosa, physicist, Bureau of Standards, 

 Washington. 



Belgium. — M. Gerard, director of the Montefiorc Electro- 

 technical Institution and president of the Consultative 

 Commission on Electricity ; M. Clement, secretary of the 

 Consultative Commission on Electricity. 



Denmark and Sweden. — Prof. S. A. .Arrhenius, Nobel 

 Institute, Stockholm. 



Ecuador. — Senor Don Celso Nevares, Consul-General. 



