June 29, 1916] 



NATURE 



361 



red dots, or letters, or some such device printed 

 on the map. This is, however, a small detail, 

 and on the whole the book is one which we hope 

 will be imitated for other holiday resorts. 



Economics: An Introduction for the General 



Reader. By Henry Clay. Pp. xvi+476. 



(London: Macmillan and Co., Ltd., 1916.) 



Price 35. 6d. net. 

 Mr. Cl.w has written a meritorious, in many 

 ways an excellent, book; but, though his style is 

 good and his reasoning clear, he has neither the 

 elevated clarity of Bagehot nor the racy charm 

 of Mr. Hartley Withers, ^'ery rightly has he 

 laid special emphasis both on the problems which 

 border the tvvo provinces of politics and ethics 

 and on such essentially vital questions as specula- 

 tion and wages. Indeed, his chapters -on these 

 last-mentioned subjects, amongst the best in the 

 book, merit the highest praise. But the pages on 

 banking, though containing an interesting dis- 

 cussion of the principles of finance, would, we 

 fear, with their continual ghb references to " runs," 

 "liquid assets," etc., prove difficult reading for, 

 let us say, a tutorial class; nor are such sen- 

 tences as : " There is an ' intensive ' as well as an 

 * extensive ' margin of cultivation ..." very de- 

 lectable nourishment for the general reader. 



The book, in fact, though in many ways an 

 excellent elementary treatise on economics, is 

 essentially academic. 



The scope of the work has already been indi- 

 cated, and includes the ordinary principles, money, 

 banking, and finance. But it is not quite clear 

 why Mr. Clay should consider that "the object 

 ... of economics is explanation solely," or that 

 "ought " must necessarily involve a moral con- 

 tent. Surely it is arguable that any teleological 

 conception may involve an appendent obligation, 

 and that economics is a normative science. May 

 we add that the absence of an index is not the 

 criterion of popularity? A. L. 



Methods in Practical Petrology: Hints on the 

 Preparation and Examination of Rock Slices. 

 By H. B. Milner and G. M. Part. Pp. vii + 68. 

 (Cambridge: W. Heff^r and Sons, Ltd., 1916.) 

 Price 25. 6d. net. 

 This little book cannot be regarded as in any 

 sense a complete exposition of the subject, but 

 it contains some useful suggestions, especially on 

 section-cutting and simple microchemical methods, 

 incuding staining. It was, however, hardly neces- 

 sary to give directions for the preparation of well- 

 known dyes, such as fuchsine, malachite-green, 

 and methylene-blue. We are even told how to 

 prepare nitroso-dimethyl-aniline, one of the sub- 

 stances employed in the production of methylene- 

 blue. Several pages are devoted to the subject 

 of the classification of rocks, which is neces- 

 sarily so briefly treated as to be somewhat mis- 

 leading in places. If these digressions had been 

 omitted, space would have been obtained for a 

 more extended consideration of the practical 

 methods with which the book is primarily con- 

 cerned. 

 [ NO. 2435, VOL. 97] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Negative Liquid Pressure at High Temperatures. 



It must have been remarked in the discussions of 

 the various forms of equation of state for vapour-liquid 

 (c/. K. Onnes and Keesom, " Ency. der Math.," 

 or in Leyden Communications, xi., 1912, p. 727) 

 that this equation should determine the range 

 of possible negative pressures in liquid. If we could 

 assume the van der VVaals form of equation to hold 

 over the wide range that is concerned, it would readily 

 follow that negative pressure could subsist only at 

 absolute temperatures below 27/32 of the critical point 

 of the substance. For water the latter is 365° C. ; 

 thus in that substance internal tension could (theo- 

 retically) persist up to 538° absolute, which is 265° C. 

 Such an order of magnitude appears at first sight 

 surprisingly high, though really there is nothing to 

 compare it with. By an oversight I have recently 

 (Proc. Lond. Math. Soc, 1916, p. 191) quoted the 

 critical point of water as 365° absolute, and so 

 obtained the much lower limit 35° C. ; and it was a 

 reference to experiments by Prof. H. H. Dixon (Proc. 

 R. Dublin Soc, 1914, p. 233), realising, for vegetable 

 sap, tensions of the order of a hundred atmospheres 

 at temperatures around 80° C, that has given rise 

 to this correction. Joseph Larmor. 



Cambridge, June 24. 



Science, Scholarships, and the State. 



All scientific men must welcome the renewed vigour 

 of the campaign for a recognition of science by the 

 State, and incidentally for the introduction of scien- 

 tific instruction into our public schools, a campaign 

 in which Nature has taken so prominent a part. I 

 have followed with the greatest interest the pronounce- 

 ments of the many eminent men on the subject of 

 science and Government published from time to time, 

 and in view of the greatness of the authorities who 

 have written on the question it is with considerable 

 diffidence that I direct attention to what seems to be 

 an oversight in many of the views put forward as to 

 the proper way to give science its due in England. 



I refer to the continued proposals to found fresh 

 scholarships for the encouragement of scientific re- 

 search, accompanied as they so often are by statements 

 as to the lack of trained men of science. In view of 

 the present (or rather, as I have no actual experience 

 of the present conditions in England, let us say the 

 pre-war) attitude of the State, the universities, and 

 private enterprise towards the men already trained, 

 it seems to me futile to make plans for training fresh 

 men until very definite steps have been taken to see 

 that there are to be recognition and scope granted to 

 them when trained. Anyone who has a knowledge of 

 1 the typical careers of the most successful (from a 

 I scientific point of view) students and younger research 

 I workers will readily understand the state of things I 

 I have in mind. If a concrete example is required, the 

 case of the 185 1 Exhibition scholars rriay be cited: I 

 choose this case as those scholarships are in the nature 

 I of State institutions. They would seem to be exactly 

 of the type intended by the advocates of the estab- 

 I lishment of new scholarships ; they are, according to 

 the conditions of award (so far as I can recollect 



