January i8, 1894] 



NA TURE 



^75 



The Measurement of Stellar Diameters.— When the 

 objective of a telescope is covered with a screen having two 

 slits in it, the image of the object under observation takes the 

 form of a seiies of fringes lying in the direction of the slits ; and 

 every one with an elementary knowledge of physics knows that 

 this appearance is due to the interference of the beams of light 

 traversing the instrument. Fizeau appears to have been the 

 hrst to point out that the size of the fringes depends upon the 

 angular dimensions of the luminous source producing them, 

 and that this fact might be utilised to determine stellar di- 

 ameters. The means by which Prof. Michelson has applied 

 the principle to the measurement of the diameters of Jupiter's 

 satellites has already been described in these columns (vol. xlv. 

 p. 160); but the suhject is so important that we give here the 

 gist of a discussion of the theory of the matter, contributed by 

 M. Maurice Ilamy to the number of the Bulletin Astronomiqiie 

 just issued. By means of Prof. Michelson's interferential re- 

 fractometer — an instrument with a life of usefulness before it — 

 it is possible to measure diameters down to o'Oi, that is, to the 

 angle which the sun would subtend if it were removed to the 

 distance of o Centauri. In fact, there is little doubt that the 

 diameters of stars are measurable by this means. All that is 

 necessary theoretically is to cover the object glass of the tele- 

 sco]ie with a screen having two rectangular, parallel slits, equal 

 and of variable width. The interference fringes produced at 

 the focus of the inslrument are made to disappear by separating 

 the slits, and when the fringes corresponding to light of a wave- 

 length represented by A have vanished, the distance (/) be- 

 tween the centres of the slits must be measured. The exact 

 formula which enables the diameter (e) of the object under ex- 

 amination to be determined from these data is, according to M. 

 Himy, 



A. 

 € = 1 '22 



/sin 1 

 There are, of course, a few difficulties in the way of perfectly 

 realising the theory, but they are being overcome, and it is not 

 too much to say that the interferential refractometer will add 

 very considerably to astronomical knowledge before the end of 

 this century. It would be interesting to measure the diameters 

 of Algol, and some of the spectroscopic binaries, and compare 

 the results with those deduced from observations of motion in 

 the line of sight. 



The Moox and Weather. — The solitary observable eflect 

 of the moon on our atmosphere was believed by Sir J. Herschel 

 to be exhibited in the tendency of clouds to disappear under a 

 Full Moon. He attributed this to the heat radiated from the 

 lunar surface. Humboldt speaks of this connection as well- 

 known in South America, and Arago indirectly supports the 

 theory by stating that more rain falls about the time of New 

 Moon than at the time of Full Moon ; the former period being 

 cloudy, and the latter cloudless, according to theory. With the 

 idea of obtaining information upon the matter, the Rev. S. J. 

 Johnson has examined the state of the sky at moonrise and at 

 midnight on the day of Full Moon only for the last fifteen years. 

 His results were communicated to the Royal Astronomical So- 

 ciety on January 12, and they confirm the opinion now held by 

 almost every astronomer, viz. that the Full Moon has no effect 

 in breaking up clouds. 



GEOGRAPHICAL NOTES. 



Mrs. Bishop (Miss Isabella Bird) has set out via Canada for 

 Korea, where she intends to spend some time studying the 

 country, and whence she may afterwards make a journey into 

 Manchuria. 



Three Christmas lectures to young people by Mr. Douglas 

 W. Freshfield, were arranged by the Royal Geographical 

 Society, and were delivered in the second week of January to 

 an interested audience. The subject was mountain-study as a 

 branch of geography, and the lectures were illustrated by a 

 large collection of extremely fine photographic views of the 

 Alps and Caucasus. 



Mr. H. J. Mackinder commenced the second series of his 

 lectures on the relation between geography and history, in 

 pursuance of the Royal Geographical Society's Educational 

 Scheme, on January 11, in the theatre of the Royal United 

 Service Institution, Whitehall Yard. The lecture was intro- 



! 



ductory to the present course, which will be continued weekly, 

 and consisted of an epitome of last yeai's lecturer, showing that 

 physical and geographical conditions largely determine the order 

 of history and the movements of peoples. The remaining 

 lectures will deal with a series of concrete examples, focussing 

 the essential features of the relation between the geography and 

 history of the chief countries of Europe, and especially of the 

 British Islands. 



The Zeilschrift of the Berlin Geographical Society publishes 

 an interesting paper, by Dr. Wegener, on the Chinese map of 

 northern Tibet and the Lob-nor District, being a sheet of the 

 official Chinese Atlis compiled by the labours of the Jesuit 

 missionaries at the Court of Pekin, who trained and superintended 

 Chinese surveyors. It was first published in 1718, and an enlarged 

 edition appeared in 1863 extending over the greater part of 

 Asia. This work still is the basis of the European maps of 

 many parts of Tibet, and the careful index of names prepared 

 by Herr Himly, which accompanies the report, is of extreme 

 value, as, not content with the Chinese lettering, he has had 

 recourse to the original Tibetan, Turki, and other native names, 

 which he transliterates with great care. 



August Artaria, the eminent Austrian map publisher, who 

 has done much to maintain the character of scientific carto- 

 graphy, died at Vienna on December 14, 1893, aged 87. 



MM. Schrader and de Margekis, whose long study of 

 the geology of the Pyrenees is well known, have contributed to 

 the last volume of the Annuaire of the French Alpine Club a 

 concise discussion of the geographical conditions of the chain 

 illustrated by a large- scale coloured orographical map. The 

 denudation of the northern slope his been much more complete 

 than that of the southern ; the tertiary strata remain on the 

 latter, but on the French side have been eroded away to form 

 the vast fans of alluvium of the lower plain. Despite their 

 general form, the Pyrenees are not composed of ranges running 

 east and west, but of mountain knots and short ranges oblique 

 to the general direction running towards E. 30' S. and then 

 turning towards E.N.E. as a rule. The mean altitude of the 

 chain is about looo metres, or say 3300 feet. Elie de Beau- 

 mont, on the assumption that the southern slope was strictly 

 similar to the northern, made his estimate of the mean height 

 500 metres greater. The mass of the Pyrenees, if spread over 

 the suiface of France, would raise the level of that country by 

 102 metres, or 330 feet. 



A NEW SULPHIDE OF CARBON 



A NEW liquid sulphide of carbon of the composition C^S.j 

 ■^^ has been isolated in a somewhat remarkable manner in 

 the chemical laboratory of the university of Buda-Pesth, by 

 Prof, von Lengyel, who contributes an account of it to the 

 current Be7-ichte. In addition to the well-known disulphide of 

 carbon, several other substances supposed to be compounds of 

 carbon and sulphur have from time to time been de-cribed ; 

 but as they appear to have been amorphous insoluble solids 

 very difficult to purify, there is very little evidence of their being 

 definite compounds. The substance now described, however, 

 appears to be a very well characterised liquid compound of 

 unmistakable odour and corrosive action upon the skin, and 

 capable of being distilled under diminished pressure. 



The method of preparing it was accidentally discovered 

 during the elaboration of a number of lecture experiments 

 illustrating the synthesis and decomposition of carbon disul- 

 phide. It was long ago pointed out by Berthelot that this 

 familiar substance decomposes at a temperature but slightly 

 higher than that at which its formation from its constituents 

 occurs. Buff and von Hofmann subsequently showed that the 

 temperature of a glowing platinum wire was ample to bring 

 about slow dissociation of the vapour, and that the disruption 

 of the compound occurred very rapidly indeed at the tempera- 

 ture of red-hot iron wire. An experiment was therefore arranged 

 to ascertain whether rapid removal of the vapour of the synthe- 

 sised compound from the heated sphere of action would largely 

 prevent the loss by dissociation, and in order that the test 

 should be a severe one, the rapidly moving vapour was subjected 

 in its passage to the high temperature of the electric arc. It 

 was during this experiment that the new sulphide of carbon was 

 unexpectedly produced. 



A little more than a hundred cubic centimetres of carbon 



NO. 1264, VOL, 49] 



