Dec. 6, 1877] 



NATURE 



99 



process. No intermediate form comes into the cycle ; 

 the yolk becomes the larva, and this latter becomes the 

 young Echinoderm ; and this larva is, according to A. 

 Agassiz, an Acalephian larva, reminding one somewhat of 

 the twin individuals of free Hydroids as Diphyes, though 

 adapted to the mode of development of the Echinoderms. 

 The Echinoderm; plutean form, with its mouth-stomach 

 intestine, and with its water system originally forming a 

 part of the digestive cavity, bearing as it would seem, 

 about the same relation to the Ctenophoras, which the 

 Ilydroid Polyps hold to the true Polyps. Therefore Agassiz 

 cannot admit that the views so frequently urged and so 

 generally admitted as to the separation of the Acalephs 

 and Polyps as a distinct type (Coelenterata) from the 

 Echinoderms have any foundation in nature. He would 

 therefore still retain the Radiate sub-kingdom with its 

 three equivalent classes — Echinoderms, Acalephs, and 

 Polyps. 



Agassiz thinks G. O. Sars' idea that Brisinga is the 

 living representative of the paleozoic starfishes rather 

 too far-fetched, and he sees no very radical difference 

 between Brisinga and such ordinary starfishes as Solaster 

 and Crossaster, and he considers that if there has been 

 a single ancestral Echinoderm, his primordial descend- 

 ants early assumed different lines of development diverg- 

 ing to a great degree, and retaining their characteristics 

 from the earliest-known geological period, E. P. W. 



VOCE US ''SPECTRUM ANALYSIS" 

 Practische Spectralanalyse irdischer Stoffe. Von Dr. 

 Hermann W. Vogel (Nordlingen : C. H. Beck.) 



'"r*HE aim of the author in writing this book may best 

 -*- be described in his own words. He says in the 

 introduction : — 



" The many^ excellent popular books on spectrum 

 analysis confine themselves chiefly to descriptions of the 

 great discoveries made by means of it ; the chemical 

 books only give short descriptions of flame reactions of 

 alkalies and alkaline earths'; they contain seldom a detailed 

 account of the methods of observation, and still less a 

 description of absorption spectra. The present work is 

 intended to fill up this want, and to be a text-book to the 

 student, and a reference book to the initiated." 



Prof. Vogel is an authority on the absorption spectra of 

 liquids and solids. Nearly half the book is given up to 

 them, and we must add the better half. Here we find for 

 the first time a connected account of all that has been 

 done on the subject. Such an account is exceedingly 

 valuable, and it brings prominently forward the gaps 

 which have yet to be filled up. Prof. Vogel treats the 

 subject chiefly from the chemical point of view, but those 

 who take greater interest in the theoretical part will also 

 find excellent information. So, for instance, the effect of 

 the solvent on the absorption spectra of solutions is dis- 

 cussed. The spectra of colouring matters are given in 

 detail, and the account of the effect of chemical reagents 

 on them will be found exceedingly interesting. There is 

 no doubt that this part of the book will be of great use to 

 every worker on the subject. 



We wish we could say as much of the chapter on 

 emission spectra. As long as the author treats of the 

 spectra of alkalies and alkaline earths, he is on safe 

 ground, but when he comes to discuss the question of 



double spectra and the spectra of gases, he is confused 

 and unintelligible. Led away apparently by a desire to 

 do justice to every writer, he quotes approvingly the most 

 divergent opinions, as if they could be consistently held at 

 the same time. He is very fond of saying that a body 

 has been proved to have two spectra but that one of them 

 belongs to the oxide or to an impurity, which is the same 

 as saying that he possesses two watches but that one of 

 them belongs to his brother. 



The author is throughout the book careless in his 

 expressipns, and this comes prominently forward in this 

 chapter. What, for instance, can the student make of the 

 following paragraph (p. 170)?— 



" A stro)ig electric spark passing throus;h air gives the 

 sped nun of oxygen together tuith that of nitrogen. Both 

 together form the so-called spectrum of air. Only one 

 spectrum of oxygen is known. In dry pure air the 

 spark only generates the spectrum of nitrogetiJ' 



The two statements in italics contradict each other as 

 they stand. One of them is true for higher pressures, the 

 other for lower pressures, but this the author has forgotten 

 to add. 



It must be said that the subject is a complicated one, 

 and even those who are practically acquainted with all 

 the experimental details would find it difficult to give a 

 connected and clear account of it. 



The first part of the book which treats of the optical 

 principles involved in the spectroscope is apparently well 

 written, and the student will find in it elementary proofs 

 of some important theorems. '^ Arthur Schuster 



OUR BOOK SHELF 



Nyassa ; a Journal of Adventures whilst Exploring 

 Lake Nyassa, Central Africa, and Establishing the 

 Settlement of '' Livingstonia^ By E. D. Young, R.N. 

 Revised by Rev. Horace Waller. With Maps. 

 (London : John Murray, 1877.) 

 This is a thoroughly interesting narrative, brisk, fresh, 

 and instructive. Mr. Young tells the story of the planting 

 of a missionary station under the united auspices of the 

 Presbyterian churches of Scotland, at Cape Maclear, on 

 the south-west corner of Lake Nyassa. Mr. Young for the 

 most part takes us over classic ground, by the Zambesi 

 and Shird, over ground familiar to readers of Livingstone's 

 earlier and his latest travels. Mr. Young in his hardy 

 little steamer the I lata, surveyed the north end of Lake 

 Nyassa for the first time, discovering on its north-east 

 shore a magnificent range of mountains, rising to from 

 8,000 to 12,000 feet above the level of the lake, and which 

 he named after his old friend Livingstone. On the 

 opposite shore is a range of less elevation. The lake is 

 marshy at the north end, subject to quite oceanic storms, 

 its shores being marked by varied and most attractive 

 scenery. The steamer caused tremendous consternation 

 among the slave-trading Arabs, who seemed to feel that 

 with the advent of a British steamer on the lake their 

 occupation was gone. The settlement was successfully 

 planted and is likely to be of service both as a centre of 

 civilisation and of more minute exploration. 



Britannia : A Collection of the Principal Passas;es in 

 Latin Authors that Refer to this Island. With Vocabu- 

 lary and Notes. By Thos. S. Cayzer, Head-Master of 

 Queen Elizabeth's Hospital, Bristol. Illustrated with 

 a'Map and twenty-nine Woodcuts. (London : Griffith 

 and Farran, 1878.) 



The title-page sufficiently describes the contents of this 



I As a personal question I may add that fhe remark attributed to me on 

 page 198 was made by Mr. Stoney and only quoted by me. — A. S. 



