1869,] Notices of Scientijic Works. 577 



scopic researches until Professor Eoscoe communicated to the 

 ' Philosophical Magazine ' Messrs. Bunsen and Kirchhoff 's paper, 

 in which they announced the probable existence of some new 

 elements discovered by its means ; but since then, spectrum obser- 

 vations have been deemed one of the most powerful means of 

 research, and have formed an intimate bond of union between 

 two sciences which before had little in common — astronomy and 

 chemistry. The book is based, as the title indicates, on a course of 

 six lectures delivered in 1868 ; but it must by no means be con- 

 cluded that the author has merely printed the lectures as delivered. 

 They are not only rewritten, but a large amount of new matter — 

 which could not well be compressed into the substance of an hour's 

 lecture — is introduced in the form of an appendix, which is often 

 longer than the lecture itself; references which were originally 

 brief are here quoted in full; discoveries which have been made 

 since the delivery of the lectures are incorporated with the text ; and 

 illustrations, whether diagrammatic or experimental, appear in the 

 form of woodcuts and chromo-lithographs. 



The first lecture is somewhat elementary, being devoted to the 

 properties of light, the action of a prism, the various conditions of 

 different portions of the spectrum, and an account of the fixed 

 black lines which cross it. In the second lecture the ordinary 

 phenomena of spectrum analyses as usually understood are de- 

 scribed, and its marvellous delicacy, which is capable of apj)reciating 

 the 180-millionth part of a grain of sodium, is enlarged upon. 

 The description of the spectroscope and its uses concludes this 

 lecture. 



The third is a continuation of the same subject, and includes an 

 historical sketch of the development of spectrum analysis, and an 

 account of the four spectrogenic metals — caesium, rubidium, thallium, 

 and indium. Some practical applications of sj^ectrum observations 

 are here given, including a very full account of the employment 

 of the sj^ectroscope in the determination of the right moment to 

 stop the blast during the Bessemer process. Speaking of this, we 

 are told that if the blast be continued for ten seconds after the 

 carbon lines disappear from the field of view, or if it be discontinued 

 ten seconds before that point is reached, the charge becomes either 

 so viscid that it cannot be poured from the converter into the ladle 

 from which it has to be transferred to the moulds, or it contains so 

 much carbon as to crumble up like cast iron under the hammer. 



Lecture IV. is devoted to the subject of the spectra of metals 

 which are only to be observed by means of the electric arc or 

 induction spark, and very carefully-reduced and well-executed maps 

 of metallic spectra accompany this subject. The concluding lectures 

 are mainly devoted to spectrum observations as applied to astro- 

 nomy, and here are given many beautiful maps and chromo-Utho- 



VOL. VI. 2 R 



