1X2 



KNOWLEDGE 



[June 1, 1898. 



will hardly enable his friends to recognize him ; but Mr. Mee 

 gives a good portrait of Prof. Adams, of Prof. Barnard, and 

 of the too little known and not sufficiently appreciated John 

 DoUond, inventor of the achromatic object glass. 



The Nests and Eggs of British Birds. By Charles Dixon. 

 (Chapman and Hall). — Mr. Charles Dixon handles his 

 subject in a scientific manner, and the book will no doubt 

 do much to develop an intelligent study of the habits of 

 birds. It is written in such simple aud attractive language 

 that it will easily be imderstood by schoolboys. Mr. 

 Dixon's plan has been to give the British breeding area 

 for every species treated of, with its breeding habits, 

 description of eggs and nest, and characteristic marks for 

 easily distinguishuig one species from another. Mr. Dixon 

 could probably have made the book still more interesting, 

 without detracting from its scientific value, if he had added 

 some more of his own observations in egg-coUecting. He 

 informs us in the preface that he has taken the eggs of 

 almost every British species, and his experiences must 

 therefore be both varied aud interesting. The volume will 

 prove a very valuable addition to ornithological literature. 



Kagsers Text Bonk of Comparative (ieohigij, — Text Book 

 of Comparative Geology, by E. Kayser. Translated and 

 edited by P. Lake. London, 1893 ; 8vo, pages xii. and 

 426, illustrated. (Swan, Sonnenschein & Co.) 



Superlatively excellent as is the geological series dis- 

 played in the British Islands, from constantly studying 

 text books which take that series as their type, English 

 students have a tendency to become somewhat " parochial " 

 in their geology, and we therefore gladly welcome an 

 elementary work on that science written from a German 

 standpoint, and now made fully available to the British 

 geologist. In saying that the book is written from a 

 German point of view it must not, however, be inferred 

 that the geology of (iermany has an undue pre-eminence 

 assigned to it ; the fact being that the different formations 

 are described most fully from the regions where they are 

 best developed. For instance, we have the chief descrip- 

 tion of the Silurian taken from Britain, the devonian from 

 the Rhenish district, the carboniferous from Britain, and 

 the Jurassic from Central Europe. 



After an introduction on the general principles of geology, 

 the various geological systems — commencing with the lowest 

 — are in turn treated historically, stratigraphically, and 

 paheontologically, the method of treatment being as broad 

 and full as appears possible in a work of tliis size. Almost 

 for the first time in an English text book we have the 

 latest views as to the nature of the archteans set fully 

 before the student, to whom it is pretty clearly suggested 

 that the complex origin of these rocks finds most favour 

 with the author. 



The illustrations of fossils in the book are both numerous 

 and well selected, aud, although not very artistic, display 

 the characteristic features of the types depicted most 

 clearly. In addition, there are numerous excellent strati- 

 graphical sections, mostly from the Continent. The 

 geologist pure and simple will perhaps not be over well 

 pleased to find the various groups of ammonites described 

 and figured under the numerous generic titles which have 

 of late years been coming more and more into use ; but this 

 is a change to which we must apparently all make up our 

 minds. 



The weakest portions of the book are those relating to 

 vertebrate paheontology, in which the author or his trans- 

 lator would have done well had they sought special advice. 

 For instance, on page 27!*, we find it stated that all 

 Jurassic mammals belong to the so-called pantotheria. 



which are affiliated (page 234) to the monotremes ; whUe 

 the Stonesfield slate is mentioned as the only English 

 horizon from which they have been obtained. Again, the 

 distinction between ichthyosaurs and plesiosaurs (page 275) 

 is decidedly badly indicated ; while on page 324 we are 

 surprised to learn that all the birds with teeth have bi- 

 concave vertebra. Further on (page 351) we are told that 

 the creodont Proviirrm is a marsupial ; while on the next 

 page the same genus is, if we mistake not, alluded to 

 among the carnivores as Protorirerra, and Hgienodon is said 

 to be allied to the hya'uas ! It is also news to us that 

 Cehochierus is a monkey (page 353) ; while even the pro- 

 verbial schoolboy probably knows that it is quite inad- 

 missible to speak of the moas as the ancestors of the 

 kiwis (page 398). 



In spite of the above faults in one particular section, we 

 can conscientiously recommend the work to geological 

 students as a well-written, compact, and, at the same time, 

 comprehensive text book, iu which the science is treated 

 on broad and philosophical views from the historical, 

 stratigraphical, aud palieontological aspects. 



Uttttrs. 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



♦ 



SIRIAX AXD SOLAR STARS. 

 To the Editor of Knowledoe. 



Sir, — I ask space for some remarks in reply to your 

 criticisms on my letter, and also on Miss Gierke's article 

 in your April issue. 



Sirian stars, are no doubt, photographically brighter than 

 solar stars of the same photometric magnitude, but I do not 

 think that this can be the explanation of Prof. Kapteyn'a 

 results as to the photographic brightness of galactic stars. 

 If the Sirian stars are more numerous in the Galaxy than 

 in other parts of the sky (which I think has hardly been 

 proved), this is at all events only true as an average result. 

 So far as I have compared the catalogues, the richest region 

 of Sirian stars (including type B of the Draper Catalogue) 

 rather runs across than stretches along the Galaxy. It 

 runs from Canis Major to Auriga. Starting from a point 

 on the Galaxy in Monocerosr, you will meet a richer Sirian 

 region by moving nearly at right angles to the Milky Way 

 than by going along it ; but Prof. Kapteyn thinks that 

 there is a continuous diminution of photographic brightness 

 as we move outwards from the Galaxy. I can find no such 

 continuous diminution of the proportion of Sirian stars as 

 we pass outwards. Mr. Marth, I think, gives all tha stars 

 within the limits examined by him which were measured 

 at less than 6'0 in the Harvard Photometry. On the other 

 hand, Prof. Pickering's Milky Way region extends consider- 

 ably beyond the limits of the Milky Way, aud includes, I 

 think, the whole of the rich Orion-Taurus region to which 

 I have already referred. But the Milky Way elsewhere 

 presents different features. In Sobieski's Shield, for 

 instance, the solar stars seem to preponderate. 



Of the brighter stars, no doubt many owe their high 

 magnitude to their great mass or intense illumination. We 

 may expect to meet with a good many of these in the Milky 

 Way, but they are not confined to it. Betelgeuse and 

 Rigel appear to be as remote as any bright star in the 

 Galaxy. Altair, CI Cygni, and ij and u Cassiopeia^, on the 

 other hand, seem to be certainly nearer to us than the 

 Galaxy, unless the true shape of the Galaxy is a disc (the 

 sun being placed in a comparative vacuity) rather than a 

 ring. If the Galaxy is a ring, I think it will be found that 

 all the solar stars which are brighter than the sixth 



