March 29, 1877] 



NATURE 



467 



paths eliding in North Africa. The fourth (D), fifth (E), 

 and sixth (F) main routes depart from the extreme north 

 of Siberia. The fourth (D) ascending the river Ob, 

 branches out near Tobolsk — one track, diverging to the 

 Volga, descends that river and so passes to the Sea of 

 Azov, the Black Sea, and thence by the Bosphorus and 

 yligean, to Egypt ; another track makes for the Caspian 

 by way of the Ural River and so leads to the Pcirsian 

 Gulf, while two more are lost sight of on the steppes. 

 The fifth (E) mounts the Jennesei to Lake Baikal and so 

 passes into Mongolia. The sixth (F) ascends the Lena 

 and striking the Upper Amoor reaches the Sea of Japan, 

 where it coalesces with the seventh (G) and eighth (O) 

 which run from the eastern portion ol Siberia and Kam- 

 chatka. Besides these the ninth (X) starting from Green- 

 land and Iceland, parses by the Faeroes to the British 

 Islands and so joining the second (B) and third (C), runs 

 down the French coast." 



All these routes are plainly laid down on the map which 

 accompanies the work, and in the absence of more pre- 

 cise information, it will hardly be in the power of any 

 British ornithologist to dispute them, though, as before 

 stated, we must hold them to be in a great measure con- 

 jectural. In the following chapters the author shows how 

 necessary it is to know the principal routes taken by birds 

 in their migrations before we can understand or reason in- 

 telligibly on their movements, and of very great interest 

 are his remarks on the Genetic Import of Regular and Irre- 

 gular Lines of Travel, and on the So-called Migratory 

 Instinct (chaps. ix. and x.), greatly amplified in the German 

 version from the brief paragraphs which represent them in 

 the Swedish original. They are, however, it must be con- 

 fessed, somewhat verbose ; but, for all that, they are well 

 worth reading. Though Herr Palmen refers to an article 

 which appeared in these columns some years ago (Na- 

 ture, vol. X. p. 415), he does not seem to be aware of the 

 theory subsequently propounded by Mr. Wallace (vol. x. 

 p. 459) as to the possible or probable origin of migratory 

 habits, wherein is expressed, in far fewer words than his 

 own, what appears to be essentially the same thing. For 

 " Migratory Instinct " Herr Palmen substitutes " Expe- 

 rience" as the piloting power, and though there is much 

 to be said in favour of this explanation in many cases, 

 others there are in which it seems to break down utterly. 

 How do the young cuckoos which stay in this country a 

 month or six weeks after their parents (whom, let us 

 remember, they have never known) have departed find 

 their way to Africa ? And how do the scores, hundreds, 

 or thousands of rapacious and wading birds, whose elders 

 do not accompany them, manage in their autumnal jour- 

 neys to arrive more or less punctually at the spot which 

 countless generations of their predecessors have reached 

 before them ? They have had no " experience," and 

 though doubtless many perish by the way, a very large 

 proportion year after year hit off exactly, and at the first 

 intention, the ancestral landing-place. What, also, can 

 " experience," which, after all, means only a knowledge of 

 landmarks, do for the species which travel by night, as 

 seems to be the habit of very many birds, or for those 

 which, like at least two of the annual visitants to New 

 Zealand, traverse a waste of waters .'' At present no solu- 

 tion of the mystery offers itself, at present such know- 

 ledge may be too wonderful for us ; but, high as it is, our 

 faith in the progress of science forbids us to say that we 

 cannot attain unto it. 



OUR BOOK SHELF 



Dyiiaviics ; or, Theoretical Mechanics, in Accordance with 

 the Syllables of the Science and Art Department. By 

 J. T. Bottomley, M.A., F.R.S.E., F.C.S. (London and 

 Glasgow : William Collins, Sons, and Co., 1877.) 



This little text-book is issued by Messrs. Collins as one of 

 their Elementary Science Series, and will prove useful to 

 beginners, by rendering them familiar, at an early stage 

 of their studies, with the more precise definitions and 

 nomenclature which have been introduced by modern 

 writers on dynamics. The distinction, for instance, 

 between the centre of gravity and the centre of inertia is 

 much more clearly pointed out than is usual in elemen- 

 tary works, and the statement that " there is only a 

 limited number of classes of bodies that possess a centre 

 of gravity " will probably be read by many with surprise. 

 The measurement, composition, and resolution of veloci- 

 ties are treated of in the chapter preceding that on force, 

 and the methods of measuring forces in terms either of 

 gravitation units or absolute units are well and fully 

 discussed. The definition of work given in the last 

 chapter might, we think, be amended. As it stands at 

 present it might lead the student to suppose that no 

 work is done by an agent moving a body, unless the 

 motion is created in opposition to a resisting force, 

 though the language employed in some of the examples 

 would be sufficient to correct such a supposition. 

 Throughout the work the author assists the student to 

 obtain " clear physical conceptions regarding the first 

 principles of dynamics," by frequently directing his 

 attention to the experimental proofs of the various laws 

 he enunciates, and by hinting at the physical, rather than 

 the mathematical, developments of his subject. 



On these grounds, we have formed a very favourable 

 opinion of Mr. Bottomley's work, and we have no doubt 

 that it will meet with the success it deserves among a wider 

 class of students than that for which it is specially 

 designed. A. R. 



LETTERS TO THE EDITOR 



\The Editor does not hold himself responsible for opinions expressed 

 by his corresponde7its. Neither can he underfake\ to return, 

 or to correspond viith the writers of, rejected mamisciipts. 

 A^o notice is taken of anonymous ccmmunications.'\ 



Evolution and the Vegetable Kingdom 



Mr. Carruthers has embodied in the Contemporary Review 

 the substance of his Presidential addresses to the Geologists' Asso- 

 ciation, on which we would ofTer a few points for consideration. 



Although not agreeing with Mr. Carruthers as to the infer- 

 ences to be drawn from the present state of our knowledge of 

 fossil vegetable remains, we cannot but admire the earnestness with 

 which he makes a stand in what we regard as a losing cause. 

 We set a high value on his researches in fossil botany, and his 

 work is characterised by unvarying and careful exactitude. What- 

 ever may be his theories, his reputation will rest on a solid basis 

 of work. Palaeontologists have to thank him for unvarying 

 kindness and readiness to aid them in their researches, forming 

 a marked exception to the treatment which botanists usually give 

 the subject. 



In discussing this question, we must keep well in mind 

 the teaching of Sir Charles Lyel), first as to the insuffi- 

 ciency of the geological record, especially with regard to 

 land-surfaces. Considering the denudation and the wasting 

 action of the waves to which remnants of terrestrial conditiors 

 are exposed during the slow process of their submergence beneath 

 the sea, and again during their gradual upheaval, it is surprising 

 to us not that so few records are preserved, but that any vestiges 

 whatever remain. Secondly, with regard to lapse of time, 

 we must get the "chill of poverty out of our bones," and not 

 misinterpret " the sign of successive events, and conclude that 

 thousands of years were implied where the language of nature 

 imports millions." Mr. Carruthers admits the imperfection of 

 the geological record, although scarcely with sufficient emphasis, 

 and compares its fragmentary condition to a tablet containing 



