16 



KNOWLEDGE. 



[January, 1904. 



"Among the Night People." By Clara D. Pierson. 

 Pp. xii. + 221. (John Murray.) .5s. — Tt may be doubted 

 whether any useful scientific purjiose is served by regarding the 

 lower animals as reasoning creatures possessed of sentiments 

 like those of human beings and a vocabulary superior to that of 

 many people. In the dainty book before us not only do 

 raccoons, rats, foxes, weasels and other " varmin " carry on 

 animated conversations, but also mosquitoes, caterpillars, fire- 

 flies and molhs. Children have no difficulty in imagining a doll 

 or rocking horse to be endowed with life, so that the stories in 

 this book will appeal to them vividly. Regarded as food for 

 imagination, comparable with fairy tales and classical legends, 

 the stories are very good and will please many young people. 

 As for natural history, well, there is a vein of it among the 

 whimsicalities described and the fine feelings pourtrayed, but 

 the pity of it is that children will be unable to discriminate 

 between what is real and what imaginary. 



"Mathematical CEYSTALLOGRAPiiy and the Theory of 

 Grouts of Movements." By Harold Hilton, m.a. Pp. xii. 

 -f- 'I6'2. (Clarendon Press.) 14s. net. — Earnest students of 

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 of a branch of the subject usually neglected in English text- 

 books. The geometrical theory of crystal structure is a 

 fascinaling field of study which the mathematician and the 

 crystallographer can explore to the mutual advantage of both. 

 From considerations of symmetry and finite groups it is shown 

 that there are onl}- thirt}'-two groups of movements consistent 

 with the law of rational indices, and therefore applicable to 

 crystallograph}'. The argument thus develops the thirty-two 

 crystal classes given in text-books on the subject. Three 

 chapters are devoted to the description of the more important 

 properties observed in crystals, and with chapters, among others, 

 on the points already mentioned, form the first part of the book. 

 The second part is devoted to theories suggested to account for 

 these properties, the methods and notation used by Schcinflies 

 in his "Krystallsysteme und Krystallstructur'' being closely 

 followed. The work of other investigators of the geometrical 

 theory of crystal structure, which may now be regarded as 

 fairly complete, is included, so that the volume is of importance 

 both for reference and as a supplement to modern text-books. 



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THE ANCESTRY OF THE HORSE. 



By E. Ly'dekkee. 



If an e.xpert mechanical engineer, totally unacquainted 

 with zoolo!:>-y and comparative anatomy, were shown for 

 the first time the skeleton of a tapir, and told that it 

 bekmged to an animal adapted to life in swamps, and were 

 then asked if he could suggest improvements in the struc- 

 ture of the bony framework in order that the animal might 

 be suited for a life on the open plains, and possess a high 

 turn of speed, there wouH be little doubt as to the nature 

 of his answer. After examining the short limbs, with two 

 ]3arallel bones in the second segment, and their three or 

 four tees each, he would at once say that it is essential to 

 lengthen all the bones of these j)ortions of the skeleton, 

 and to reduce the width of the foot either l)y diminishing 

 the size of all the toes except the large middle one (which 

 would have to be proportionately increased), or by doing 

 away with them altogether. He might fiu-ther suggest 

 that it would be imjjortaut to lengthen the bones of the 

 lower segments of the limbs (except, of course, the three 

 terminal ones) to a much greater extent than tlie upper 

 one. And if he were specially inventive he might also point 

 out that a much greater stride and far more mechanical 

 power would be gained, if the animal could be made to 

 stand only on the extreme tips of its toes, so that the 

 whole of the hinder portion of the foot would be raised 

 above the ground. Puitlier. he might also advise that it 

 would confer strength and solidarity on the limbs if the 

 two bones in the second segment of each were welded 

 together, so as to form but one. 



If. moreover, he were told tliat the tapir is probably a 

 short-lived animal, which feeds on soft marsh vegetation, 

 and tliat it was essential to olitain an animal whose span 

 of life should be from fifteen to twenty years, and whose 

 food should consist of dry grasses and grain, he would 

 naturally look at the molar teeth of the tapir. Tliese he 

 Would find to have low crowns surmounted merely by a 

 few simple ridges ; and if the skeleton belonged to an old 

 individual, he would not be long in discovering that some 

 or all of them were worn nearly or quite down to the roots. 

 Obviously his answer would be that the crowns of the 

 teeth must be very considerably lengthened ; and, more- 

 over, so constructed as to be more capable of resisting wear, 

 and better adapted for grinding hard substances than are 

 those of the tapir. 



After this inspection of the skeleton of the tapir, we 



