458 



NA TURE 



[September x2, 1895 



•complete. It forms the best monograph on the subject 

 yet written. The origin of petroleum is so treated as to 

 present the various theories put forvvard to account for 

 its occurrence ; necessarily, no authoritative decision can 

 be griven on this ver)- debatable question. Concerning 

 the occurrence of sulphur in the petroleums from Ohio 

 and Canada, those interested would do well to supplement 

 the bare mention of the fact here given by reference to 

 the July number of the/owr/W of the Franklin Institute, 

 where C. F. .Maber\- gives an account in which the 

 •subject is treated as its importance requires. Warren is 

 stated by Mr. Redwood to have isolated hydrocarbons of 

 the C„H^„ series, termed naphthenes by Markownikoff. 

 Mr. Maberj- shows that the Ohio and Canadian petro- 

 leums do not yield the naphthenes of Markownikoff and 

 Ogloblin, but give hydrocarbons of the C„H2„-+ ■, scries of 

 similar boiling points. This writer also proves con- 

 •clusivcly the presence of benzene, toluene, and xylenes in 

 these petroleums. ■ 



The manufacture of shale oil gives yet another instance 

 of the application of continuous processes ; the te.\t con- 

 tains very lucid descriptions of these, well and sufficiently 

 ■JUustraied. Few of the general public can have any 

 adequate conception of the number and variety of lamps 

 in existence for use with oils. An exhaustive account is 

 given of these, and the advantages or disadvantages 

 ■characteristic of the mam types of oil-lamps are dwelt 

 upon at sufficient length to enable an intelligent judgment 

 to be formed as to the suitability of any particular lamp 

 for the work required from it. 



The .Section on safety-lamps, with which this volume 

 concludes, has been contributed by D. A. Louis, in con- 

 junction with Boverton Redwood. It gives by no means 

 the least interesting reading. Although the excellent 

 account of the lamp-indication of fire-damp is highly 

 technical, and calculated to be eminently useful to 

 specialists, the general reader will find no difficulty in 

 grasping the principles involved, and will much appreciate 

 the clearness with which this important subject is treated. 



It may be hoped that the high standard exhibited in 

 this volume will be maintained in volume iii., announced 

 as to appear shortly. The editors are certainly to be 

 •congratulated on the excellent production now before us. 



N\". T. 



OUR BOOK SHELF. 



Science Readers. By X'incent T. Murche. Hook iv. 



Pp. 216. fLondon : Macmillan and Co., 1895.) 

 Thk conversational method of instruction, which used 

 to be so general in school books, is not one that leads 

 to pleasant memories. Mr. Murch^ has created two boy 

 prodigies in his "Science Readers," and they ask and 

 answer questions of a teacher whose laudable ambition 

 is to elii.it and impart all kinds of scientific know- 

 ledge upon every suitable or unsuitable occasion. We 

 revi-rcn' e that teacher for his patience and for his ability 

 to find texts in ever>'thing. The pity of it is, that lessons 

 given m this way on all and sundry topics lack the quality 

 whi' h lies at the base of all true scientific knowledge, 

 viz. the orderly arrangement of facts. \ lesson on 

 solids, liquids, and gases precedes one on our br lies, 

 another on gravity precedes a lesson on vertebrates and 

 invertebrates. A lesson on the classification of inverte- 

 brates is wedged between two on hydrostatic pressure, 



NO. 1350. VOL. 52] 



and so on throughout the book. Possibly the variety is 

 introduced to charm the youthful mind, but it is not a 

 desirable attribute of the book ; for the method must 

 result in the acquisition of unconnected information, and 

 such knowledge has little to commend it. In the matter 

 of illustration, and simplicity of language, the book leaves 

 little to be desired. 



A Giirdoi of Pleasure. By E. \*. B. Pp.220. (London: 

 Elliot -Stock, 1895.) 



A FEW chapters fresh with the fragrance of common 

 countrj- flowers, and breathing the life of " lustrous 

 woodland." Here and there the authoress lapses into 

 sentiment, but, taken as a whole, her language is 

 attractive in its simplicity. The changes that go on in 

 organic nature from month to month are drawn with 

 careful touch, and many students of botany would derive 

 benefit from the contemplation of the sketches. 



On the Temperature Variation of the Thermal 

 Conductivity of Rocks. 



Naturk reproduces the results obtained by Lord Ki-lvin, 

 P.R.S.,andJ. R. Erskinc Murray, a paper read at the Rnyal 

 Society, May 30, " On the Tcniperalure Variation of the Thermal 

 Conductivity of Rocks." These gentlemen arrived at the following 

 rosulls : " (§ '3)^ • • • that for slate with lines of fluor parallel to 

 cleavage planes, the mean conductivity in the range from 123' C. 

 to 202' C. is 91 per cent, of the mean conduclivily in tlie ran^e 

 from 50" C. to 123° C, and for granite the mean (-onilurtivity in 

 the range from 145" C. to 214" C. is 88 percent, of the mean 

 conduclivily in the range from 81" C. to 145° C." 



These results are so widely different from those I obtained 

 by another method, and which Lord Kelvin had the kindness to 

 publish in Naturk, March 7, 1S95, p. 439, that I must be 

 aIlo\vc<l to intro<hice here a wor<l of objection. 



It seems to me that details of experimental dispositions are 

 important cnou);h. and should be trustworthy. It is however, 

 not opportune to ibscuss them minutely now. 



The experimenters lased their work on the case of Fourier's 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of refected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. '\ 



The "i4026^5'j" Line and Dj. 



Mav I call attention to the f;»ct that the line at 4026'5, now 

 recognised as belonging to the spectrum of helium, and con- 

 spicuous in the Orion stars, is also prominent in the S])ectrum of 

 the solar chromosphere. -Vlthough not given in the catalogue 

 of chromosphere lines (which dates from 1S72), it was observed 

 and published as long ago as 18S3 (Am. four. Sci. and Art., 

 November 18S3), in connection with another line at 4092, seen 

 at the same time. Since then the 4026 line has been observed 

 repeatedly, and might be given a place in the catalogue with a 

 relative frequency of about 15, and a brightness of 3 or 4. Like 

 the other helium lines it has no dark analogue in the ordinary 

 solar spectrum. The 4092 line frills upon a strong double line 

 shown uiwii Rowland's map, but I am not sure to which of the 

 two comjjonents it belongs ; it is faint, antl seldom seen. 



While D3 rarely ajipcars as a dark line upon the solar spec- 

 trum, yet in the course of over twenty years I am able to count 

 up a considerable number of instances ; certainly not less than 

 twenty or thirty. The jihenomenon occurs usually in the 

 penumbral region of an active sun-spot, which in its nucleus 

 reverses the lines of hydrogen, magnesium, and sodium, and 

 sometimes D3 itself. By a slight motion of the telescope as one 

 passes away from the nucleus, it crosses regions where Dj 

 appears as a smoky shade : on i>age 130 of " The Sun " I have 

 figured a typical case. i_ 



I have not yet been fortunate enough to .sec the duplicity ol 

 D3 myself, but Prof. Reed has observetl it on several occasions. 



Hanover, N.H., .Vugust 26. C. A. VoUNC. 



