512 



NATURE 



[October 19, 191 1 



the metals mined, a value of 2,508,200;. having been 

 recovered in 1910. It occurs chiefly as free gold, but 

 alloyed with a varying quantity of silver, and is found 

 disseminated through various rocks, e.g. granite 

 syenite, granulite, various schists, ironstone, and 

 quartzite; but quartz veins traversing various rocks 

 are the dominant gold carriers, all situated close to 

 the granite contact. These veins vary greatly in 

 width, and also in yield, the average yield for 19 10 

 being 30J. yd. per ton milled. 



Nearly all the mines are situated on old native work- 

 ings, and the quantity of gold taken from these 

 workings, which sometimes attain a depth of over 

 200 feet, must have been considerable. 



The blunders of pioneer mining companies and re- 

 sultant financial difficulties have furnished a rich 

 harvest for tributers, who have made handsome profits. 



In a large number of the reefs a serious falling off 

 in values is encountered at the water level, their 

 payability down to that point apparently being due to 

 secondary enrichment. 



The conditions of Rhodesia are not favourable to the 

 formation of extensive alluvial deposits, and very 

 little gold has been derived from that source. 



Other metals than gold are coming increasingly into 

 prominence. Chromite has been mined continuously 

 and with a progressive output since 1905 from a hill 

 of the mineral at Selukwe, the output in 19 10 being 

 44,000 tons, of a value of 98,130?., most of the mineral 

 being shipped to America. 



Wolfram and scheelite have been produced in the 

 Buluwayo and Hartley districts of a total value of 

 10,930?. 



Nickel and cobalt have not been found, but the 

 author describes their mode of occurrence and the 

 characters of the minerals at Sudbury and New 

 Caledonia as a guide for prospectors. 



Copper ores are very widespread in Rhodesia, and the 

 author describes the Kansanshe, Bwana M'Kubwe, and 

 Lnikondo and Alaska deposits, on all of which there 

 have been extensive old workings, those on the Alaska 

 extending in an almost unbroken line for about 1700 

 feet with an extreme width of 660 feet, and have been 

 proved to go down in some places to a depth of at 

 least 70 feet. The copper so far exposed is mainly in 

 the form of malachite, the sulphide zone not having 

 yet been reached. It is disseminated through a 

 crushed belt of limestone. 



Lead and zinc are found as an enormous body in the 

 well-known occurrence at Broken Hill, which is 

 remarkable for the large development of phosphates 

 of lead and zinc within the zone of oxidation. The 

 Penhalonga Gold Mine has yielded lead as a by- 

 product. 



Molybdenite occurs on the farm Appingadam. Bis- 

 muth and antimony have only as yet been found in 

 Rhodesia with the gold ores rendering- them refrac- 

 tory. The output of silver is obtained mainly as a by- 

 product in the treatment of gold ores, and partly from 

 the argentiferous galena of the Penhalonga Mine, but 

 no true silver minerals have as yet been found. 



A chapter is also devoted to the non-metalliferous 

 minerals of Rhodesia, which, while interesting, space 

 NO. 2190, VOL. 87] 



does not permit us to notice, and the book concludes 

 with a chapter giving hints to prospectors which they 

 will find of interest. 



Generally speaking, the book is clearly written, and 

 contains a good deal of information ; it should be 

 in the hands of anyone who is devoting his attention 

 to prospecting in Rhodesia. 



THE FOUNDATIONS OF SCIENCE. 



Die logischen Grundlagen der exakten Wissen- 

 schajten. By Prof. Paul Natorp. Pp. xx + 416. 

 (Leipzig and Berlin : B. G. Teubner, 1910.) Price 

 6.60 marks. 

 Probleme der Wissenschaft. By Federigo Enriques. 

 Uebersetzt von Kurt Grelling. Erster Teil, Wirk- 

 lichkeit und Logik. Pp. x + 258 +16. Price 4 marks. 

 Zweiter Teil, Die Grundbegriffe. Pp. vi + 259-599. 

 Price 5 marks. (Leipzig and Berlin : B. G. Teub- 

 ner, 1910.) 

 r PHE publication of these works, and, indeed, of 

 -L the whole series to which they belong, furnishes 

 further evidence for the revival of the interest in the 

 ultimate problems of science, an interest which be- 

 comes very much alive so soon as an important branch 

 of investigation reaches the borders of the knowable, 

 and stands in danger of losing itself in unphilosophic 

 disputations. Such an event is at present taking place 

 in physics in connection with the relativity hypothesis, 

 and before we reach the end of the controversy the 

 logical foundations of science will have been tho- 

 roughly overhauled. 



Prof. Natorp's work is practically a treatise on the 

 fundamental principles of mathematics. It deals with 

 such subjects as infinity and continuity, direction and 

 dimension as determining pure number, time and 

 space as mathematical structures, and the temporal 

 and spatial arrangement of events. The treatment of 

 the problems touched upon is detailed and thorough, 

 and often leads to very decided (and, let us hope, 

 decisive) pronouncements on present-day problems, as 

 when the author declares it to be impossible to decide 

 between the Euclidean or non-Euclidean structure of 

 our space by means of any imaginable physical ex- 

 periments. A brief summary of the new Principle of 

 Relativity as formulated by Lorentz, Einstein, and 

 Minkowski concludes a very informing and valuable 

 work. 



Prof. Enriques 's two volumes are more practical 

 and empirical, and will probably appeal to a wider circle 

 of readers than Prof. Natorp's. The style is vigorous, 

 and sometimes distinctly informal, and for that very 

 reason the book is more readable than is the average 

 work on these recondite subjects. His definition of 

 "reality" is interesting. "Our belief in the reality of 

 a thing," he says (p. 85), "supposes a totality of 

 sensations which follow invariably upon certain con- 

 ditions arbitrarily provided." This, as the author 

 himself perceives, does not eliminate the possibility of 

 a complex hallucination, unless we assume that the 

 will is entirely in abeyance during hallucination. 

 Those who prefer to regard reality as simply the 

 "hallucination" eommon to the majority of mankind 



