so 



NATURE 



[March 9, 1916 



duced the author to adopt his particular treat- 

 ment, the effect is to give his work a somewhat 

 disjointed structure. The treatment is slight and 

 "sketchy," and at times inadequate. It is irra- 

 tional, for example, to dismiss the work of twenty 

 centuries in about as many lines, but this is prac- 

 tically all the space that is given to ancient and 

 alchemistic chemistry. To say that the study of 

 chemistry begins with the work of Boyle is on a 

 par with Wurtz's famous statement that it owes 

 its origin to Lavoisier, and is equally untrue. 



Dr. Lowry's book, in spite of occasional slip- 

 shod writing, is interesting reading, and the stu- 

 dent, if already furnished with a little chemical 

 knowledge, will pick up much information con- 

 cerning certain broad features in the development 

 of the science since the middle of the eighteenth 

 century. The illustrations of classical apparatus 

 are a valuable feature, although we are unable to 

 see the relevancy of the pictures of crystallised 

 minerals and salts taken from the national collec- 

 tions in the British Museum. They are like the 

 tropes and metaphors which King James depre- 

 cated in the sermon — "brilliant wild flowers in the 

 field of corn, very pretty, but of no particular 

 advantage to the corn." 



RELATIVITY AND ELECTRONS. 

 Relativity and the Electron Theory. By 

 E. Cunningham. Pp. vii+96. (London: 

 Longmans, Green and Co., 1915.) Price 45. 

 net. 



THE principle of relativity has gradually 

 acquired a fundamental position in 

 theoretical physics, and the appearance of an 

 introductory monograph on the subject will be 

 welcomed by all who wish to have a knowledge 

 of its essentials. The present work, as stated 

 in the preface, is written with the purpose of 

 setting out as clearly as possible the relation of 

 the principle to the generally accepted electron 

 theory. Only quite elementary mathematical 

 analysis is employed throughout the book; those 

 who wish to penetrate more deeply in the subject 

 being referred to the author's larger work on 

 "The Principle of Relativity." 



In the latter part of the book the principle of 

 relativity is presented from Minkowski's point of 

 view. The four-dimensional form of relativity is 

 of very great importance, partly on account of 

 its elegance and simplicity, but also because of 

 its suggestiveness in the present transition 

 stage of dynamics. Unfortunately, only a short 

 outline of the four-dimensional vector analysis of 

 Minkowski and his disciples is given. On p. 72 

 NO. 2419, VOL. 97] 



examples of 4-vectors are given in a form which is 

 open to criticism. The point-instant (x, y, a, t) is 

 called a 4-vector. It would be more satisfactory 

 to denote the 4-vector by (x, y, z, ict), since ict 

 and not t is actually the fourth component of the 

 vector in question. A similar remark applies to 

 K (ux, Uy, Ug, i) (on the same page), which should 

 be written k (m^, i*y, «2, ic), in which form it would 

 be consistent with the equation at the foot of 

 P' 75. viz. : 



(Sx, S^, S^, S„) = p(U., U,„ U„ u)jc. 



The quantity denoted by "k" is, in consequence 

 of a printer's omission, imperfectly defined. The 

 author introduces four-dimensional vectors in the 

 " New Mechanics " in an excellent way by show- 

 ing how they serve to unify the two aspects of 

 "force" as the "time rate of change of 

 momentum " (Galileo) and " space rate of change 

 of energy " (Huygens). One of the charac- 

 teristic features of Minkowski's presentation of 

 the principle of relativity is its capacity for unify- 

 ing or reconciling different and, in some case&, 

 apparently contradictory aspects of phenomena. 



In the final chapter the author outlines the 

 way in which the "objections of those who 

 demand a real aether to carry real effects " can 

 be met. 



The work is one of considerable merit, and 

 provides a really good and sound introduction to 

 the subject with which it deals. W. W. 



THE HANDWORKING OF IRON AND 

 STEEL. 



Forging of Iron and Steel. By W. A. Richards. 

 Pp. viii + 219. (London: Constable and Co., 

 Ltd., 191 5O Price 65. 6d. net. 



THE title of the above work is somewhat mis- 

 leading, in that its scope is much narrower 

 than is suggested by the title. Apart from a short 

 chapter at the end on steam and power hammers, 

 it deals only with hand-forging in its various 

 aspects. The book, which is stated to ]ye intended 

 both for the "high-school boy" and the "veteran 

 smith" — it is written by an American — opens 

 with a chapter on the historic use of iron and 

 steel from early periods. It then deals in brief 

 review with the smelting of iron ores and the 

 production of cast irons, wrought irons, and 

 steels, the author stating that it is unnecessary 

 to go deeply into the subject of metallurgy or to 

 introduce metallurgical theory. We are told (on 

 page 20) that the air pressure in the blast furnace 

 is from 15 to 25 lb. per square inch. No doubt 

 in the hard-driven American furnaces, where 



