358 



NATURE 



[May 19, 192 1 



only being placed in each box, then the various 

 complicated problems which result when the 

 restrictions are removed, and finally the general 

 problem of distributing 5 different sets of similar 

 objects of which there exist p-^ of one kind, p^ of 

 a second kind . . . and />, of another kind, into 

 boxes of which there are m^ of one kind, va^ of 

 a second kind . . . and rrit of another kind, 

 the whole number of the boxes being any num- 

 ber not greater than the whole number of the 

 objects. 



It is a great achievement to expound a difficult 

 subject in a simple manner, and for that reason 

 alone Major MacMahon is to be congratulated. 

 For some reason which is not at present clear, the 

 theory of the combination of different sets of 

 similar possibilities (which can conveniently be 

 represented as the distributions of balls in boxes) 

 is of the utmost importance in many different 

 branches of science. For example, it is clear 

 that this theory must enter into such a question 

 as the formation of a muddy liquid from mole- 

 cules which occur in groups of one, two . . . n. 

 The theory will also be relevant in a serious con- 

 sideration of error in relation to causal laws. 

 The subject is, therefore, of great importance in 

 applied as well as in pure mathematics, and 

 might very well prove another example of the extra- 

 ordinary way in which abstract mathematics 

 leads the way in applied science. 



Dorothy Wrinch. 



]\ Regime delle Acque nel Diritto Pnhblico e 

 Privato Italiano. By Aw. Antonino Vitale. 

 Pp. x + 480. (Milano: Ulrico Hoepli, 192 1.) 

 25 lire. 

 The rapidly increasing development of the water- 

 power resources of Italy since the commencement 

 of the war, and the probability of still further ex- 

 tensions in its use in the future, have led many 

 writers in Italy to attempt a clear exposition of 

 the legal aspect of the question, which is an ex- 

 tremely wide one, covering, as it does, the in- 

 terests of the State, communities, and individuals. 

 The author of the present work. Advocate Vitale, 

 who is attached to the Ministry of Public Works, 

 brings to his study a special competence. After 

 a reasoned consideration of the question whether 

 there exist private waters in contradistinction to 

 public waters, or whether there is a private title 

 to certain waterfalls as compared with the public 

 title, he deals at length with the legal aspects of 

 private title. The question of administrative con- 

 trol is treated in three large sections, the first of 

 these bearing on the harnessing of water-power and 

 the protective measures involved ; the second on 

 the actual utilisation and control of falls, rivers, 

 and streams ; and the last on contentious points 

 of law and administration. In this survey all 

 possible applications of water-power, including 

 hydro-electric stations, irrigation plants, river di- 

 versions for water supply, transport, etc., have re- 

 ceived consideration. The volume contains copi- 

 ous references to existing legislation on the sub- 

 ject and to the works of other authors. The main 

 NO. 2690, VOL 107] 



interest of the book is naturally to Italians,, 

 although, of course, existing and subsequent 

 enactments would affect corporations and syndi- 

 cates anywhere which might anticipate obtaining 

 concessions for the development of water-power 

 in Italy. E. S. H. 



A Text-book of Physics. By Dr. W. Watson. 

 1 Seventh edition. Revised by Herbert Moss. 

 j Pp. xxvi-t-976. (London: Longmans, Green,, 

 and Co., 1920.) 215, net. 



The new edition of this well-known text-book is. 

 substantially a reprint of that of 1919. The addi- 

 i tions made include the spherometer, Young's ex- 

 tensometer, the McLeod gauge for measuring low 

 pressures, and the travelling microscope. The 

 discussion of Young's modulus, Poisson's ratio, 

 and rigidity has also been considerably ampli- 

 fied, while descriptions of the pyrheliometer, the 

 Callendar continuous-flow method of mixtures, and 

 the Beckman and clinical thermometers now find 

 a place. Further additions include a proof of 

 Gauss's theorem with illustrations, likewise illus- 

 trations of the applications of Kirchhoff' s laws, and 

 in electron theory a concise account of "canal" or 

 positive rays. The explanation of diffraction 

 through a slit has been extended, and "resolving 

 power " is also treated. 



The values of physical constants have been re- 

 vised, and under "Terrestrial Magnetism" the 

 majority of the maps and diagrams replaced by 

 recent plottings. It is interesting to note there- 

 from that the east line of zero declination, or 

 agonic line (1917), now consists of a nodal curve 

 with intersecting branches, in place of the former 

 simple curve and Siberian oval, as in 1907. 



In its present form W^atson's "Physics " is the 

 most comprehensive single-volume text-book of 

 physics in the English language. It contains little 

 that may now be adversely criticised, and the com- 

 pilers have improved the index by increasing it to- 

 nearly twelve pages. A. W. Bain. 



La Colloidotherapie : Rdsultats Cliniques. By Dr. 



J. Laumonier. (Collection Medicale.) Pp. 



ii-!-283. (Paris: F^lix Alcan, 1920.) 5-50 



francs. 

 This book, as its title suggests, has been written 

 by one who has no doubts as to the answer to a 

 question which gives pause to many— namely^ 

 whether any special therapeutic value can be 

 assigned to preparations of metal and other sub- 

 stances in the colloidal state which can be at- 

 tributed to their state. 



The theoretical section is commendably brief,, 

 the main body of the work being devoted to a 

 systematic account of the method of preparation, 

 uses, and physiological action of colloidal solutions 

 of silver, gold, platinum, arsenic, etc. 



The author's reading is limited, and his refer- 

 ences are confined practically solely to the work of 

 his compatriots ; but the work of the French 

 school affords ample material for the object in 

 view — namely, the production of a book of refer- 

 ence for the practitioner. 



