Feb. 8, 1872] 



NATURE 



287 



a hollow sphere of lead by Francis Bacon. Again 

 " Mariotte's Tube," as it is called (p. 120), is described 

 and figured by Robert Eoyle fourteen years before 

 Mariotte mentions it. Morren's mercury pump for slow 

 but accurate exhaustion is described and figured on 

 p. 141 (Figs. 3, 4) ; by its means a vacuum of one-tenth 

 of a millimetre of mercury may be obtained. 



The Acoustics has been considerably augmented, for 

 while in the 1S68 edition it occupied fifty- two pages, it 

 now fills fifty-five larger pages. We notice, among 

 other things, an account and woodcut of Konig's stetho- 

 scope, and of his cylindrical resonator ; of Helmholtz's 

 apparatus for the synthesis of sounds ; and various new 

 woodcuts of manometric flames. We do not observe any 

 mention of singing or sensitive flames. In the section 

 devoted to heat, we do not find an account of Prof. 

 Guthrie's experiments on the conduction of heat by 

 liquids ; or of the recent observations regarding the heat 

 of the moon and certain stars ; and the portion relating 

 to the "Mechanical Equivalent of Heat" is still very 

 meagre and insufficient. 



The magnetism of iron ships might with advantage be 

 alluded to in the account of Magnetism ; and M. Noe's very 

 powerful thermo-electric battery is also worthy of notice. 

 On pp. 596 and 597 we are glad to observe capital figures 

 and descriptions of the electrical machines of Bertsch 

 and Carre ; the latter appears to be a most desirable 

 addition to the Physical L.aboratory, as, even without a 

 condenser, plates of 49 centimetres diameter give sparks 

 18 centimetres long, and the machine is not much 

 affected by moisture. The apparatus figured on pp. 

 67S — 670 for demonstrating the attraction and repulsion 

 of electric currents by currents, consists of new and 

 improved forms of those devised by Ampere, and is 

 extremely ingenious ; as is also the form of solenoid 

 described on p. 690. (Fig. 5.) 



A few alterations in the te.xt would be advisable if a 

 table of errata is introduced ; thus (p. 750) no explanation 

 is given of the stoppage of a cube of copper when caused 

 to rotate between the poles of a powerful electro-magnet, 

 as soon as the magnet is made ; neither is reference given 

 to the explanation which in another form is given else- 

 where. Again (p. 628) we read : — ..." Kirchhoff 

 has concluded that the motion of electricity in a wire in 

 which it meets with no resistance is," c&c. A very few 

 clerical errors are observable : — p. 185, M. Costa should 

 be M. Colli ; p. 246, topmost line, " substances by which 

 their action," &c., should read " -ui/iic/i /y their action ; " 

 p. 289, line ten from the top, p should be/'; and p. 524, 

 line 4, we find '■■plain polarised light." 



These, however, are quite minor matters ; the book 

 was a good one at the outset of its career, and each suc- 

 ceeding edition has rendered it more and more complete. 

 The above remarks are made rather as suggestions than 

 in any spirit of adverse criticism. Ganot's Physics is a 

 great addition to our scientific literature, and neither 

 student nor savaitt could spare it from his library. 



G. F. RODWELL 



THE SOLAR ATMOSPHERE 



T^HE object of the investigation discussed in N.\TURE 

 ^ (No. loi, pp. 449-452) being merely that of ascer- 

 taining whether the incandescent matter contained in the 

 solar atmosphere transmits radiant heat of sufficient 

 energy to admit of thermometric measurement, no par- 

 ticular statement was deemed necessary regarding the 

 spectrum which appeared on the bulb of the focal thermo- 

 meter after shutting out the rays from the photosphere 



during the experiments. The appearance of this spectrum 

 has in the meantime been carefully considered. Its 

 extent and position suggest that the depth of the solar 

 atmosphere far exceeds the limits hitherto assumed. 



The accompanying illustration represen'.s an apparatus 

 constructed by the writer to facilitate the investigation. 

 Evidently the expedient of shutting out the photosphere 

 while examining the effect produced by the rays emanating 

 from the chromosphere calls for means by which the sun 



