REVIEWS 507 



The book is written simply, clearly, and lucidly, yet with never an inexact or 

 slipshod phrase. The many striking analogies used in illustration are all true 

 to fact, and, as was remarked of one of Mr. Gibson's earlier books, "facts have 

 not been surrendered to make the book interesting, but the interest has been 

 built out of the facts." The volume has been made as interesting as many a 

 book of adventure by an imaginary trip which the author and his readers take 

 together in a wonderful flying machine (reminiscent of Jules Verne) to see the 

 moon and the various planets and what they are like. If we have any criticism 

 to make of the treatment adopted, it is chiefly that it shows a slight want of 

 balance, too large a portion of the book being devoted to our own solar system 

 in comparison with that devoted to the stars in general, to nebuke and to the 

 other wonders of the heavens. Apart from this, the subject is well surveyed. 

 We must confess, however, that we find the illustrations poor and disappointing. 

 Astronomy is a subject which lends itself particularly well to numerous and 

 good illustrations, and authors will find astronomers ready to assist them in 

 this matter. Mr. Gibson's book would have made an even greater appeal to 

 children had more care been taken in this respect. Some plans also of the 

 best known constellations would have been valuable, for children's interest greatly 

 increases when they are able to pick out different stars or constellations in the 

 sky. In perusing the book, we have noticed a few slips which have entered, 

 in spite of its general accuracy. On page 147 Jupiter is said to have nine 

 moons, one of which has a retrograde motion, whilst on page 237 we are told 

 eight ; the correct number is nine, but two (including the recently discovered 

 ninth satellite) have retrograde motion. The temperature of the sun is consider- 

 ably understated, and the paragraph on the number of stars is poor. We 

 mention these in no carping spirit, for Mr. Gibson has evidently been at some 

 pains to avoid errors, and they in no way affect the general excellence of the 

 book. We commend it to all parents and teachers and hope that it will be 

 widely circulated amongst young people. 



H. S. J. 



PHYSICS 



Surface-Tension and Surface-Energy and their Influence on Chemical 

 Phenomena. By R. S. Willows, M.A., D.Sc, and E. Hatschek. Re- 

 printed from "The Chemical World." [Pp. viii + 80, with 17 illustrations.] 

 (London : J. & A. Churchill, 191 5. Price 2s. (yd. net.) 



The chemistry of colloids has, especially within recent years, assumed so great 

 importance not only from a theoretical but also from a technological standpoint 

 that more and more time and attention are being devoted to its study. There is 

 more than one book available at the present time which deals with the subject of 

 colloid-chemistry from what we may call the experimental scientific side, and there 

 are several publications dealing exclusively with the technical applications of the 

 subject, e.g. in reference to bleaching, dyeing, pigments, filtration, rubber, cement, 

 soils, etc. The present volume has another purpose in view, namely to give as 

 clear an account as may be of the fundamental physical concepts upon which the 

 subject rests. Without such a groundwork, it is hardly likely that the research 

 chemist will really grasp the significance of the phenomena with which he deals. 

 It is obviously essential that with such a purpose in view the writing must be that 

 of a physicist. The authors responsible for the work are eminently qualified to 

 carry it out successfully. The only regret one has is that it has been deemed 

 necessary to make the treatment so brief and in securing simplicity of presentation 



