January 28, 1892] 



NA TURE 



291 



we should have been equally impressed with its insigni- 

 ficance—and yet the two statements are virtually the 

 same. In fact, the unscientific reader is not likely to 

 realize the prodigious number of pounds in the earth's 

 mass. 



It may be remembered that Croll computes, in " Climate 

 and Ti;ne," the value of the eccentricity of the earth's 

 orbit from Leverrier's formulae, and endeavours thus to 

 assign actual dates to various glacial periods. Now, Sir 

 Robert Ball very justly will not admit that our knowledge 

 of the solar system is accurate enough to justify the ap- 

 plication of these formulas to the enormously long inter- 

 vals of time involved. I think, however, that it would 

 have been of interest to the general reader to be told in 

 round numbers the kind of intervals which we have 

 reason to believe may have elapsed between one glacial 

 period and the next ; in fact, to learn whether the intervals 

 are probably millions of millions of years, or hundreds 

 of thousands of years. I conjecture that our knowledge 

 of the planetary movements is sufficient to enable us to 

 say that such an interval may be something comparable 

 with 200,000 years. I should like, further, also to ask 

 Sir Robert Ball whether he does not consider that Le- 

 verrier's formulae may probably be relied on to give at 

 least a rough approximation for about 100,000 years in 

 the past; and, if this is so, whether we might not conclude, 

 with fair probability, that the last glacial period occurred 

 about that number of years ago ? I must, however, dis- 

 claim any special knowledge on this point, and I should 

 gladly see his opinion, or that of any other physical 

 astronomer, on the matter. 



In conclusion, I wish to say that, in making the fore- 

 going criticisms and suggestions, I have no intention of 

 disparaging the book ; on the contrary, it is only because 

 it is a good book that it is worth while to consider it 

 carefully. I have found it profoundly interesting from 

 end to end, and I am convinced that it will be widely 

 read, as it deserves to be. G. H. Darwin. 



POPULAR ZOOLOGY. 

 Am»ut! Sketches. By C. Lloyd Morgan, F.G.S., Prin. 

 cipa' :^f University College, Bristol. (London : Edward 

 Arnold.) 



THIS is one of those delightful books of natural 

 history for young people which their parents never 

 had the benefit of, and for which they ought to be duly 

 thankful. A competent naturalist here gives them the 

 result of his full and varied knowledge, but gives it so 

 blended with imagination and humour, so intermingled 

 with anecdote and personal adventure or observation, as 

 to make it a real story-book about animals, by reading 

 which we learn much of their lives and habits, their 

 peculiarities of structure and their relations to each other, 

 while we seem to be only reading for amusement. There 

 is nothing systematic in this volume. It is merely a 

 collection of miscellaneous chapters on a variety of 

 animals, beginning with the lion and ending with the 

 oyster, every chapter of which is both pleasant and 

 instructive. 



The best way to notice a book of this kind is to give a 

 few examples of the author's style, which in this case will 

 NO. I 161, VOL. 45] 



certainly commend the book better than any description 

 of its contents. First, then, as a bit of serious biology,' 

 we will give a passage on the nesting-habits of the 

 ostrich. 



" The nest is scooped out in the sand, and two or 

 three hen-birds may combine to lay their eggs in it, to 

 the number of about twenty. It is said, and that by 

 several observers, that, besides the eggs laid in the nest, 

 each hen lays several in the neighbourhood, and that 

 these are broken when the young are hatched, and the 

 contents are given them as food. But I am inclined to 

 regard these statements with some suspicion. The hens 

 take turns in sitting during the day, never leaving them 

 long in the scorching heat of the South African sun. But 

 at sun-down the cock-bird takes charge of the eggs, and 

 sits throughout the night. He is not going to be bound 

 by any conventional rules as to the proper division of 

 labour between the sexes. 



" A very careful observer, Mrs. Barber, has drawn 

 attention to the fact that the indistinct grey colours of 

 the hen ostrich are wonderfully adapted for purposes of 

 concealment. These birds while upon their nests do not 

 erect their necks, but place them at full length in front of 

 them upon the ground ; and the grey-brown body might, 

 Mrs. Barber says, be easily mistaken for some other 

 object, such as, for instance, an ant-hill, so common 

 on the plains of South Africa. That so large a bird 

 should be inconspicuous may seem surprising; but 

 another observer, Mr. W. Larden, tells us of his ex- 

 perience with the rhea, or South American ostrich, which 

 seems quite to bear this out. ' One day,' he says, * I 

 came across a rhea in a nest that it had made in the dry 

 weeds and grass. Its wings and feathers were loosely 

 arranged, and looked not unlike a heap of dry grass ; at 

 any rate the bird did not attract my attention until I was 

 close on him. The long neck was stretched out close 

 along the ground, the crest feathers were flattened, and 

 an appalling hiss greeted my approach. It was a pardon- 

 able mistake if for a moment I thought I had come across 

 a huge snake, and sprang back hastily under this im- 

 pression.' 



" The male ostrich, with his splendid black and white 

 feathers, would not be thus inconspicuous by day. But 

 he sits at night, and his strength and pugnacity would 

 induce most other creatures to let him alone. Mrs. 

 Barber describes the careful manner in which the female 

 bird approaches the nest in the morning, when her turn 

 for incubation has come. In wide circles, and apparently 

 in the most unconcerned manner, she will feed round the 

 nest, never once looking towards it, but gradually ap- 

 proaching nearer and nearer to it by diminishing each 

 circle as she walks round, until at length her perambula- 

 tions have brought her to within a yard or so of the nest, 

 when the birds will rapidly change places, the male 

 walking swiftly away, and not remaining in the vicinity 

 of the nest during the day. The wonderful rapidity with 

 which the change is effected is perfectly astonishing, and 

 it is impossible to see the exact manner in which it is 

 done, so swiftly do they change places." 



As an example of Mr. Lloyd Morgan's lighter manner, 

 what can be more attractive than the opening sentences 

 of his chapter entitled " Long-nose, Long-neck, and 

 Stumpy " ? 



" 'And which of all the animals in the Zoo do you like 

 best .? ' I said to a bright, fair-haired little girl whom I had 

 assisted in her descent from the elephant. 



" * I think I like Long-nose, Long-neck, and Stumpy 

 best, because they are so big and curous, and Long-nose 

 best of all because he has given me a ride. Did you 

 know it was his nose ? ' 



" Of course I affected the most extreme surprise and 



