350 



NATURE 



\Aug. 29, 1872 



stitution of the sun ; this problem is so difficult, that 

 it is necessary to leave to every one the responsibility 

 of his own ideas on this subject. I ask, then, for per- 

 mission to decline any critical notice of this part of the 

 book. 



I must mention also a useful description, illustrated 

 with maps, of the telluric and atmospheric lines from 

 the works of Brewster, Gladstone, Angstrom, and Jansscn. 

 The remaining part of the book is entirely devoted to 

 the most delicate applications of spectrum analysis toastro- 

 nomy. A preliminary description of the sun-spots, facukcj 

 and other pecuharities of the surface of the sun,of the promi- 

 nences round the disc, and so on, is given before the 

 spectroscopic process for analysing these appearances 

 is introduced, and enables the reader to understand very 

 well the difficulties of the problem and the interest of its 

 solution. I must mention especially the interesting account 

 of the three total solar eclipses of 186S, 1S69, 1870. A 

 large series of drawings and photographic fac similes 

 give the best idea of the phenomena, and show the 

 improvements due to photography and spectroscopy ; the 

 relatively great extent devoted to this account is justified 

 by the importance of the subject ; the spectrum analysis 

 of the prominences is in fact one of the most considerable 

 results obtained for a long time in the sciences of 

 cosmogony. 



Now from this discovery of Janssen's it is easy to observe 

 every day the solar prominences by utilising the bright 

 lines of their spectrum. Janssen's method, discovered in 

 India soon after the eclipse of 1 863, was independently 

 discovered again some weeks after by Lockyer, who has 

 the real merit of announcing two years before the 

 possibility of such an important observation, and 

 would very likely have had the honour of priority if he 

 had had beforehand the material means of carrying out 

 his designs. 



Schellen's book contains a complete account of the im- 

 proved telespectroscopes of Lockyer, Respighi, Secchi, 

 Huggins, Janssen, Young and Z( lUner, and a beautiful series 

 of coloured sketches, representing some daily observa- 

 tions of prominences all varying, but truly characteristic of 

 their form. I must confess, however, that some of those 

 beautiful pictures seem to me rather too much embellished 

 by the imaginative fancy of one of the observers. The 

 sun-spots and facuht^ observed with a telespectroscope 

 give a good number of new facts which have led Lockyer 

 and Secchi to the most important inductions upon the 

 constitution of the sun. 



The spectroscope, as it is known, is able to give an 

 exact measurement of the proper velocity of the luminous 

 bodies. A German physicist, Doppler, deserves to be 

 mcittioned as the first who called the attention of astro- 

 nomers to this subject, though a good number of his 

 assertions may be incorrect. After him, Fizeau, a French 

 physicist, to whom we are indebted for the first determi- 

 nations of the velocity of light on the surface of the earth, 

 showed the errors of Doppler in a little paper not very 

 well known, published in 1S49 (" Bulletin de la Societd 

 Philomatique de Paris"), and calculated the apparent 

 change of refrangibility which would be produced by the 

 proper motion of some heavenly bodies ; but no direct ex- 

 periment was made before the complete application of 

 spectrum analysis to the sii.!ereal phenomena. In this 



way Schellen's book gives a good abstract of the works of 

 Huggins and Secchi. In these researches the velocity of 

 rotation of the sun was to be tested as a verification of 

 the general law of the phenomenon. I ought to say, that, 

 the rather discordant results want a theoretical analysis, 

 because the problem seems to me, in the case of the sun, 

 more complicated than it appears at first sight. How- 

 ever, the inlluence of the velocity of the gas streams, 

 especially of hydrogen, which constitute the greater part 

 of the prominences, is unquestionably verified by 

 Lockyer's observations. In the same way Huggins has 

 proved and determined the proper motion of Sirius by 

 the apparent change of refrangibility of the F line. 



The remaining part of the book is devoted to stellar 

 and meteoric spectrum analysis. It is impossible to give 

 a superficial notice of the beautiful researches of Huggins 

 and Secchi, researches which are always going o\\ ; the 

 reader will find with interest various important results of 

 these studies — for instance the existence in many stars of 

 a good number of terrestrial substances — hydrogen, 

 nitrogen, magnesium, sodium, (S:c. 



One of the most interesting facts is the observation of 

 thetempoiary star which appeared in May 1866 ; the great 

 brightness of the star was due, as indicated by the spectro- 

 scope, to an immense mass of incandescent hydrogen. 



At the end of the work the author gives some very im- 

 portant observations of Huggins and others on the 

 spectrum of ncbute ; the chief result is the possibility, 

 with the aid of the spectroscope, of distinguishing by 

 the composition of their light the true nebula; from the 

 clusters of stars. 



Finally, a description of the spectrum of the aurora 

 borealis, the identification of its bright lines with some 

 bright lines of the solar corona, a description of various 

 meteors, lightnings, and their spectra, show into what diffi- 

 cult objects this new branch of science has pushed its 

 investigations. 



On the whole, this book must be considered as a good 

 type of a " popular work ; " it deserves the attention of 

 the public, and the esteem of scientific men ; and finally, 

 it recommends itself by a gracious side. It was trans- 

 lated into English by two ladies, who have had the double 

 merit of giving a proof of their good scientific taste, and 

 of showing an example of the help which their sex is able 

 to afford to science. CoRNU 



OUR BOOK SHELF 



Health and Con fort in Housc-buildini;. By J. Drysdale, 

 M.D., and J. W. Hayward, M.U. (London : E. and F. 

 Spon, 1872.) 



Sewcr-gas, and liaiv to keep it out of HonsiS. By Osborne 

 Reynolds, M.A. (London : Macmillan and Co., 1872.) 



The first of these works supplies a want long felt by 

 that section of the public who are desirous of obtain- 

 ing a good supply of fresh air in their houses, without 

 being subjected to the cold draughts usually associated 

 with almost every system of ventilation. The book is 

 most carefully written, and is evidently the result of much 

 thought, time, and intelligent labour. After reviewing 

 very fairly the systems of ventilation which have been 

 proved to be ineffectual for supplying fresh warm air to 

 the whole of a house, although pcihaps very appropriate 

 for single rooms, we are told that the key-note of this new 



