318 Reviews — Br. J. H. Poynting — The Earth. 



If our German friends would orfsjauize a staff and get another 

 ' Bronn ' ready for the next generation thqy would be doing a real 

 service to Paloeontology, but we honestly think that work published 

 in parts in this way is of little or no service to the real worker, 

 especially when it is arranged in systematic and not alphabetical 

 order. It is never wise to introduce into a reference book any 

 personal idiosyncrasies. 



VI. — The Earth : its Shape, Size, Weight, and Spijt. By J. H. 

 Poynting, Sc.D., F.E.S. 8vo ; pp. 141, with 49 text-figures. 

 Cambridge: at the University Press, 1913. Pricels.net. 



DIFFERENT branches of geology have been dealt with in previous 

 volumes of this enterprising series, and Professor Poj-nting's little 

 book is concerned with tlie earth from a physical aspect. There are 

 only three chapters, and their simple-sounding titles are : " The Shape 

 and Size of the Earth," "Weighing the Earth," and " The Earth as 

 a Clock." In telling the story of the growth of the idea of a round 

 earth, the author would take us to the top of a hill on a clear day to 

 look over a stretch of lowlands, where we might with the ancients 

 conclude there was nothing to suggest that the earth is not flat. In 

 our first chapter we are told how a different conception of the earth's 

 form came into being, and how Columbus proposed to reach India by 

 sailing to the west. A few simple figures and some easy calculations 

 are given in support of the modern view, and these are followed by 

 a description of the method of measuring distances on the earth's 

 surface. The base-line method of measuring is illustrated also by an 

 account of the finding of the distance of the nearer stars. 



In beginning his second chapter the author illustrates clearly the 

 relationship between the weight and mass of the earth. We then 

 read of the earth-weighing experiments — the early ones of Newton, 

 Bouguer, Maskelyne, and Cavendish, and the later and more delicate 

 one of Professor Boys. When considered as a clock, our planet is 

 regarded, of course, as whirling round the sun, and we see how the 

 spin of the cyclones is connected with this movement. The principle 

 of Foucault's pendulum is also dealt with. But by far the most 

 interesting topic is that of the tides, which are treated in connexion 

 with Sir George Darwin's discoveries. It is shown that the tides are 

 gradually reducing the earth's spin, that the action of the moon on 

 them is gradually lengthening the day, and the reaction of them on 

 the moon is lengthening the month. The same reckoning points to 

 the probability of the moon and the earth forming the same body 

 in the past, and the likelihood of the moon's ending her journey by 

 reunion with the parent globe in the far-distant future. 



YII. — Effects of Pkessuee and Temperature on Rock-formation. 



GEOLOGICAL speculations on matters connected with the formation 

 of rocks have often been founded on misunderstood or mis- 

 interpreted experiments. Mr. John Johnston and Mr. L. H. Adams, 

 in a paper on the effect of high pressures on the physical and chemical 

 behaviour of solids, published in the number of the American Journal 



