34 



KNOWLEDGE. 



[Februaev 1, 1899. 



By far the cominonest meteorites, however, are those 

 called " sporadosiderites," in which small specks of nickel- 

 iron lie scattered through a ground composed of silicates. 

 Ordinarily, certain structures are present, notably the 

 globular crystalline aggregates called chomlni, which were 

 produced in the mass by some special conditions of con- 

 solidation. The minerals present, however, are in general 

 those of our own basic igneous rocks. A number of sub- 

 stances regarded as peculiar to meteorites may yet be found 

 in the deeper parts of the earth's crust. Even the strange 

 form of silica, asmanite, so carefully separated by Story- 

 Maskelyne from the meteorite of Breitenbach in Bohemia, 

 is now believed to be identical with the mineral tridymite, 

 which occurs in the ca\'ities of so many terrestrial lavas. 



Whether the internal core of the earth is a liquid under 

 great pressure, or whether it is a solid mass, it is certainly 

 of much higher density than the ordinary rocks of the 

 outer crust. Mr. J. H. PoyntLng* has recently reviewed 

 the long series of researches by which the mean density of 

 the earth has been determined. Among the results, none 

 stand out more prominently than those achieved by 

 Cavendish with the torsion-balance in 1798. We now 

 know that, while the crust has a mean density of about 2-6, 

 the earth as a whole has a density of 5'5 ; and the simplest 

 explanation of this is that the denser materials are accumu- 

 lated within, while the lighter ones float, as it were, on 

 the outside. The crust, by which we mean that part 

 accessible to ourselves, is of trifling thickness ; already we 

 seem to be within touch of the basic masses which underlie 

 it, with their included blocks of metal. In Greenland and 

 New Zealand, for instance, we find brought up to us the 

 layer corresponding to the "sporadosiderites" of space; 

 and at Ovifak we seem to have glimpses of an actual iron 

 core, corresponding to the metallic meteorites. 



Is such a core an improbability — a core in which iron 

 predominates, but in which other native metals may lie 

 abundantly dissolved ? Astronomers agree that the 

 meteorites, drawn from time to time to the surface of the 

 earth, belong to swarms circling in the solar system. 

 The remarkable uniformity in their characters points to 

 one of two things ; they either originated in the disruption 

 of a single planetary body, or else the great mass of extra- 

 terrestrial matter is far more basic, far more rich in 

 native iron and nickel and cobalt than are the common 

 rocks of the earth's crust. Both these suggestions may 

 be true ; they do not contradict each other. In the 

 meteoric bodies that were, by some astronomical " acci- 

 dent," sent flying into space, we may find the best repre- 

 sentatives of the inner layers of our earth. At present 

 our attention becomes more and more directed to the 

 olivine-rocks, the serpentines, the " picrites," and their 

 allies, which here and there break through the crust, 

 bringing up such a wealth of nickel-ores and iron-ores 

 from below. The contents of such masses, particularly 

 any nodular groupings that appear to differ from the 

 ordinary rock, must be scrupulously examined. We are 

 as yet only feeling our way on the outskirts of the unseen 



core. 



♦ 



j^ott'cts of Boolis. 



> 



The Ploy 0/ Animals : a Study of Animal Life and Tnstincl. 

 By Prof. Karl Groos. Translated by Elizabeth L. Baldwin, with 

 a preface and an appendix by Prof. J. Mark Baldwin. (Chapman 

 & Hall.) 10s. 6d. Observations of the vaiious activities of 

 animals are of deep interest, and their value in tracing the course 

 of psychological development cannot be over-estimated. But the 



• " The Mean Density of the Earth," ariffin & Co., 1894. 



tendency to consider all exhibitions of animal intelligence from 

 an anthropomorphic point of view — and it is difficult to do 

 otherwise — makes it essential to exercise extreme care in 

 such observations, so that the acts shall be described without 

 consideration as to the possible why and wherefore of their 

 performance. Popular volumes on natural history topics often 

 contain instances of the more human, but less scientific style of 

 recording observations. In the present work, however, a sound 

 and thorough statement of the facts and observations referring 

 to one of the phases of animal intelligence is presented, and 

 we think that few outdoor naturalists would fiiil to derive 

 benefit from an examination of them. More than this, we 

 will say that before valuable observations of animal psychology 

 can be made, the naturalist must be acquainted with the 

 contents of a volume of this kind. Prof. Lloyd Morgan has 

 done yeoman service in the same field in his various works on 

 the habits and mental processes of animals ; and the course of 

 mental evolution is traced in Romanes's works. We have also 

 ^Ir. Arthur Thomson's popular book on various aspects of 

 animal life, and Houssay's work on the industries of animals. 

 Prof. Groos's volume deals with quite a distinct aspect of 

 animal activit}', and supplements all that have preceded it. 

 The anecdotes of intelligence in animals recorded in it have 

 been selected with discrimination from a vast store, and their 

 bearing upon biology and animal psychology is clearly pointed 

 out. Play is regarded as a real instinct, and Mr. Herbert 

 S])encer's theory that it represents '" surplus energy " is discussed 

 and abandoned. The observations described, the classification 

 adopted, and the interpretations suggested command attention, 

 and Prof. Mark Baldwin's notes give additional value to them 

 all. As a contribution to the literature of animal life, in which 

 the transition from animal to human intelligence is indicated, 

 the volume should be cordially welcomed. 



Creation Records. By George St. Clair. (David Nutt.) 

 10s. Gd. The theory which was put forward some time ago by 

 Sir Norman Lockyer to explain the foundations of Egyptian 

 mythologj' by astronomical considerations is brought into 

 prominence again by Mr. George St. Clair. The idea of the 

 book, briefly expressed, is tliat the myths of Egypt are all 

 related to one another, and are neither separate fables nor idle 

 fancies. That they reveal, moreover, a religion intimately 

 dependent upon the stars, and tell a true story of astronomical 

 progress and theological changes before the time of our written 

 histories. But wliile the conclusions and explanations are very 

 fascinating, they can be by no means accepted as final expressions 

 of the exact state of things. Many archsologists who have 

 studied the question from their point of view are not prepared 

 to admit the conclusions. It seems as if one idea has got com- 

 plete hold of Mr. St. Clair, and, like Mr. Dick and King 

 Charles's head, it wiU keep on appearing at most inopportune 

 moments. There is no doubt that observations of the sun and 

 stars plaj-ed a very important part in the worship of ancient 

 Egypt, and that Mr. St. Clair's book is fuU of interesting state- 

 ments made on good authoritj-, but the best work suffers when 

 it is evident that a preconceived notion has dictated many of 

 the conclusions. 



Aids in Practical Geology, By Prof. GrenviUe A, J. Cole, 

 M.R.i.A. (Griffin & Co.) 10s. 6d. Third edition, revised and 

 enlarged. We have examined the third edition of Prof. Cole's 

 well-known book with great pleasure. Former editions have 

 been a companion to all serious students of geology for more 

 than eight years, and have been instrumental in clearing up 

 many a difficulty and saving much valuable time. Prof. Cole 

 is really practical. The student can turn to his book and learn 

 where some necessary instrument can be obtained, and how 

 much it will cost. He is given fatherly advice as to how to 

 pack specimens, and the best way of getting them home. He is 

 carefully conducted through the maze of petrological terminology, 

 and has the chief morphological and other characteristics of 

 typical fossils pro])erly emphasized. The third edition has been 

 thoroughly overhauled. Recent editions to the equipment of 

 the geologist, such as the diffusion-column of Prof. Sollas, are 

 described ; also new methods of observation, like the mode of 

 determining relative refractive indices devised by Dr. Becke. 

 Similarly, in view of the present state of zoological classification, 

 the ])alsontological sub-divisions of former editions have been 

 somewhat relaxed. We commend this volume to all students of 

 geology, for no one of them can afford to be without it. 



