Supplement to "Nature" February 5, 1903. 



IX 



with the question must be chagrined to think that a 

 solution so obvious should have escaped them. The 

 author tells us that when he 



"first began to read on this subject, he had a precon- 

 ceived opinion of the cause, which to him seemed so 

 reasonable that he wondered why others had not come to 

 the same conclusion." 



Ah, but that is always the way ! It is only after the 

 riddle is solved that it seems so simple — but the 

 apparent simplicity of the solution should not detract 

 from the merit of its perspicacious discoverer. 



We give, in a few words, Dr. True's inspired "theory" : — 

 Up to and during part of the Tertiary period, the earth 

 had so far cooled and the crust had become so thickened 

 that it was just able to support itself. 



" But finally the point was reached when it could sustain 

 it (the pressure) no longer. The last grain of sand broke 

 the camel's back." 



Suddenly the floor of the ocean settled down, while 

 the mighty north and south mountain ranges of the 

 globe were ridged up. Concurrently with these move- 

 ments, the polar regions were elevated into dry land, and 

 their supply of warm water from the south being cut off, 

 the formation of ice-fields forthwith began and finally 

 culminated in the Glacial period. The Arctic lands then 

 existed as plateaus — miles in height — an amount of 

 elevation 



" amply sufficient to produce almost any degree of cold, 

 and also a slope extending several hundred miles, suffi- 

 cient to account for the motion of the ice in a southerly 

 direction. Here is where the northern elevation, which 

 nearly all geologists say must have accompanied the 

 Glacial period, comes in. The great wonder is that they 

 have not seen what caused it." 



It is needless to say that under such conditions the ice 

 continued to accumulate until not only all N. Europe and 

 N. America, "but the whole bottom of the N. Atlantic 

 as far south as the southern border of the telegraph 

 plateau," were covered with an ice-sheet. While this 

 mighty ice-sheet overwhelmed those regions, N. Asia 

 escaped glaciation. Why? Simply because it was 

 deeply submerged at the time, and so the polar ice ad- 

 vancing southwards broke off in icebergs and floated 

 over north and south Siberia. The withdrawal of so 

 much water from the ocean and the piling of it up in 

 the form of ice on the western hemisphere naturally dis- 

 turbed the earth's equilibrium. We should not be sur- 

 prised, therefore, to learn that all of a sudden the 

 earth "tipped" or "toppled over," in order to bring 

 about "a readjustment of matter to the stationary axis." 



"N. America and W. Europe moved down out of the 

 cold region, while N. Siberia, on the opposite side of the 

 earth, moved up into it." 



Of course, these changes produced a cataclysm— 

 " great tidal waves, perhaps miles in height," sweeping 

 the ice-sheet out of the N. Atlantic and flooding much of 

 the continents. 



And so the Glacial period came to an end in N 

 America and Europe. But, as our author remarks, 



"it is plain that when the west side of the earth warmed 

 up, the east side became cold, and it is also plain that the 

 transition was sudden." 



NO. 1736, VOL. 67] 



This is shown by the admirable preservation in N. 

 Siberia of the carcasses of mammoths and woolly 

 rhinoceroses — " the congeners of those now inhabiting a 

 tropical climate." 



" It seems that when the east side of the earth tipped 

 northward, the reaction caused a great tidal wave that 

 caught the animals which roamed over the regions south 

 of and adjacent to the then northern ocean, and carried 

 them away as drift, to become frozen in ice, and there 

 they have remained ever since." 



Who will not sympathise with glacialists ? Their oc- 

 cupation, alas! is gone ; no more difficulties are left for 

 them to encounter ; with a wave of his magic pen, our 

 inspired doctor has banished darkness and laid bare 

 every secret of the Ice Age. He knows the past of our 

 globe so well that one cannot wonder he should be 

 equally confident as to its future. His theory is a true 

 " open sesame." The same succession of remarkable 

 changes which he has unveiled for us will, we are assured, 

 again supervene ; and his readers may well shiver and 

 shudder at the "gloomy picture " he presents for their 

 contemplation. They are advised, however, by the con- 

 siderate author not to be "uneasy" because of that 

 dismal future — it is still a long way ahead. " They will 

 not be here when it comes." J. G. 



PROPERTIES OF MATTER. 

 A Text-Book of Physics. By J. H. Poynting, Sc.D., F.R.S. 

 and J. J. Thomson, M.A., F.R.S. Properties of 

 Matter. Pp. vi + 228. (London: C. Griffin and Co., 

 Ltd., 1902.) 



THIS volume is to be regarded as the opening one of 

 a series forming a text-book of physics, of which 

 the second part, namely, " Sound," was published some 

 two years ago and is now in its second edition. The 

 remaining volumes, dealing with " Heat," " Magnetism 

 and Electricity," and " Light," will be published in suc- 

 cession, it may be hoped at somewhat shorter intervals. 



The book is not intended for elementary students on 

 the one hand or for mathematicians on the other, and 

 the authors make a welcome innovation in entirely 

 omitting the more purely mathematical side of mechanics 

 with which text-books on the properties of matter are 

 usually encumbered. After a brief preliminary chapter 

 dealing with the experimental evidence for the constancy 

 of weight and mass, about fifty pages are devoted to a 

 most interesting and complete account of the experi- 

 mental work on the measurement of the acceleration of 

 gravity, the figure of the earth and the constant of 

 gravitation, introducing the student to a number of most 

 instructive physical methods, described with the discri- 

 mination of a practised experimentalist who has made a 

 special study of the subject. The next seven chapters 

 (60 pp.) deal with the elasticity of solids from an experi- 

 mental standpoint, mathematics being introduced only so 

 far as is necessary to permit a comparison of theory and 

 observation in a few simple cases, which serve to illus- 

 trate the physical principles involved. Many compara- 

 tively recent experiments are described, such as those of 

 Ewing on the yielding of crystalline substances by 

 slipping along the cleavage planes. The remainder of 



