5 8o 



NATURE 



[August 7. 191; 



matrix an expression he calls its determinoid. 

 i his is. in fact, a sum of maximum determinants, 

 taken from the matrix, with a rule of sign 

 for each. There can be no doubt of the value of 

 the theory oi matrices, and that a good book on 

 the subject is a desideratum. Whether the notion 

 of a determinoid is likely to be anything like so 

 valuable is a doubtful question, and we confess 

 that we would rather have had a treatise on 

 matrices alone. The present volume ends with a 

 chapter on the solution of any system of linear 

 equations, anil to read this first of all is perhaps 

 the best way to become favourably impressed by 

 the treatise. The earlier i hapters seem rather 

 diffuse, and contain a large number of new techni- 

 cal terms, some of which, like "corranged," are 

 not at all attractive. The next volume will contain 

 applications to algebra and geometry, besides . 

 discussion of matrix equations of the second 

 degree. When this appears it will be easier to 

 form a judgment on the work as a whole; mean- 

 while, we can see that it contains a great deal of 

 valuable matter expressed in one consistent nota- 

 tion. (,. B. M. 



OUR BOOKSHELF. 

 Brands Used by the Chief Camel-owning Tribes 

 of Kordofan. (A Supplement to "The Tribes 

 of Northern and Central Kordofan.") Bv H. 

 A. MacMichael. I'p. viii + 40 + xvii plates. 

 (Cambridge University Press, 1913.) Price 

 6s. net. 



NEARLY thirty years ago Robertson Smith 

 lamented that no good collection of miasm (the 

 tribal marks with which every Arab tribe brands 

 its cattle) had been made, and now Mr. Mac- 

 Michael has published as a pendant to his history 

 of the Arab tribes of Kordofan a collection of the 

 marks used by these tribes as camel brands. The 

 utility of such a work to the members of the 

 Sudan Civil Service is too obvious to need accentu- 

 ation, but there is also a good deal of scientific 

 interest attaching to it, although the writer's ex- 

 perience in the Sudan makes him regard it as im- 

 probable that the high hopes cherished by Robert- 

 son Smith will be realised, that such collections 

 will enable us to trace the ancient history of the 

 people. 



Xo doubt each tribe, or each section of a nomad 

 tribe, once had a distinctive brand, but it seems 

 that in many cases this has been lost, or at least 

 has fallen into disuse. The brands themselves 

 are for the most part named after common objects, 

 such as bersham, the "cross-hilt of a sword," and 

 ba'b, "a door," while others derive their names 

 from the part of the camel which is branded ; thus, 

 bakkai, derived from the word meaning " to 

 weep," is applied to a linear vertical mark below 

 the eye, because it is here that tears trickle down. 

 Generally the brand is hichlv conventional and 

 XO. 2284. VOL. 91] 



unlike the object it represents, but in a few cases, 

 though simplified, it retains all the essentials of 

 the original, as, e.g., the rig! el ghorab, a "crow's- 

 foot," used by some of the negroid "Arabs " of the 

 northern hills. 



Rainfall Reservoirs and Hater Supply. By Sir 

 A. R. Binnie. Pp. xi+157. (London: Constable 

 and Co., Ltd., 1913.) Price 8s. 6d. net. 

 Ix the application of exact meteorological observa- 

 tions to practical life, the utilisation of rainfall 

 records by the waterworks engineer takes a fore- 

 most place. Rainfall is moreover among the most 

 important of the natural resources of a country, 

 and it is fitting that Sir Alexander Binnie should 

 put together the results of his wide experience in 

 a book which will impress the townsman with this 

 tact in its more direct association with his daily 

 life, in addition to giving to the engineer a survey 

 of the problem with which he is faced, and of the 

 methods of dealing with it. 



The first chapter treats of the measurement of 

 rainfall and the variation in amount from vear to 

 year and place to place ; diagrams are given to 

 show how the total fall increases as the ground 

 rises, and emphasis is laid upon the fact that in 

 a region with a prevailing wind direction the 

 maximum rainfall frequently occurs on the lee 

 sice of the high ground. Another diagram illus- 

 trates the approach of the average annual rain- 

 fall to a normal value as the number of years in- 

 creases ; thus one year may be 50 per cent, above 

 or 40 per cent, below the normal, but the average 

 of ten years is not likely to differ by more than 

 10 per cent, in either direction from the normal 

 value. 



The next chapter deals with the flow from the 

 ground, floods, and evaporation, about which our 

 knowledge is very deficient owing to the scarcity 

 of trustworthy records. Subsequent chapters are 

 devoted to the methods of calculating the avail- 

 able supply, the construction of reservoirs, and 

 the arrangements for conveying the water from 

 the source and distributing it to the users. There 

 is much that is technical naturally in these 

 chapters, but the subject is treated in such a way 

 that even the details are made interesting, and 

 their importance for safety or economy is clearl) 

 shown. E. G. 



Planetologia. By Ingegnere Emilio Cortesc. 

 Pp. vii + 387. (Milan: L : lrico Hoepli, 1913-) 

 Price 3 lire. 



Ix view of the fact that nearly 300 pages are 

 taken up with terrestrial phenomena, and only 

 eighty pages are devoted to the remaining 

 members of the solar system, the title " Planeto- 

 logia " scarcely seems suitable for the present 

 book. Perhaps the author could not think of a 

 more suitable title. 



The book contains an exposition of some of the 

 main physical properties of the earth's crust, the 

 age of the earth, its past geological history, the 

 theories of tides, earthquakes, volcanoes, the 

 origin of the earth's atmosphere, and the principal 



