January 28, 19 15] 



NATURE 



;85 



account of the two-stream theory, based mainly on 

 Prof. Edding-ton's own researches, is given. The 

 mathematical foundation of this theory and of 

 Schwarzschild's ellipsoidal hypothesis is placed 

 in a separate chapter, an excellent arrangement 

 from the point of view of the general reader. The 

 unmathematical reader must also pass over much 

 of the statistical investigations in chapter x., 

 though to the mathematician the application of 

 the theory of integral equations to statistics will 

 be particularly interesting. Except in these two 

 sections the general reader should have no 'great 

 difficulty in following the main line of the argu- 

 ment. Other chapters deal with those remarkable 

 phenomena which are associated with the spectral 

 classification of the stars, and which constitute the 

 most significant discoveries in recent astronomy ; 

 the difficult problem of counting- the stars in the 

 sky according to magnitude, based largely on 

 recent work at Greenwich, but paying perhaps an 

 exag^gerated respect to a well-known memoir of 

 Kapteyn ; and finally, the attempts which have 

 been made to explain the stellar system in dynami- 

 cal terms, attempts which seem rather premature 

 in view of our still imperfect knowledge of the 

 kinematical relations. 



In conformity with the editorial scheme of the 

 series to which it belongs, the book convevs 

 throughout a strongly personal view, from which 

 at some points the reader may be tempted to differ. 

 But it is on the whole an eminently sane view, and 

 this means much when in the nature of the case 

 provisional judgments alone are possible. Ideas 

 are in a state of flux, and gratitude is due to Prof. 

 Edding-ton for fixing- the phase of the moment in 

 a permanent, accessible form. H. C. P. 



THE ENAMELLING INDUSTRY. 

 The Raiv Materials for the Enamel Industry and 

 their Chemical Technology. By Dr. J. Grun- 

 wald. Translated by Dr. H. H. Hodgson. 

 Pp. viii-r225. (London: C. Griffin and Co., 

 Ltd., 1914.) Price 85. 6d. net. 



THE preparation of enamels for the purposes 

 of ornament dates from a very remote 

 period ; we find them in use in ancient Egypt and 

 Babylon, although in the earliest known sf>eci- 

 mens they were used as inlays in the metal objects 

 they adorned, and not melted on them until some- 

 what later times It is not, however, until the 

 beginning of the nineteenth century that the coat- 

 ing with enamels of iron hollow wares, saucepans, 

 and the like for domestic use was practised, a 

 process thaT many years afterwards was applied 

 to the enamelling- of iron in sheets and plates. 

 The materials deali with by the author are those 

 NO. 2361, VOL. 94] 



employed in the manufacture of enamels for these 

 purfwses on a commercial scale. 



The economic importance of the industry on 

 the Continent is evident, if we consider that it 

 gives employment in Germany to 25,000, and in 

 Austria-Hungary to 19,000, persons ; and a large 

 part of the output finds a market in England. 



The appearance of a translation of Dr. Grun- 

 wald's book is opportune at the present time, 

 when methods are being discussed for the satis- 

 factory organisation of our industries and the 

 equipment of works, with the object of producing 

 articles which hitherto have largely or entirely 

 been made in other countries. 



Its perusal brings forcibly to our notice the part 

 which science has played, and is playing-, in the 

 management and control of the processes of the 

 enamelling- industry, and that complete success 

 can only be attained by the co-operation of science 

 and practical skill. Much scientific investigation, 

 however, is still needed before certain hindrances 

 to the success of many of the op>erations of the 

 enameller can be successfully grappled with. 



The object of the book is to supply those en- 

 gaged in enamelling works with an account of the 

 composition, properties, and limitations of use of 

 the various materials employed and of their prac- 

 tical application on a large scale. An exact 

 knowledge of these, it is scarcely necessary- to 

 point out, is absolutely essential in order to over- 

 come the difficulties which often arise in works' 

 procedure. 



Much of the information contained in the book, 

 it may be said, can be found in works on min- 

 eralogy and applied chemistry, but it is so 

 scattered that, for purposes of reference, it is 

 practically inaccessible to the busy worker. 



The chief materials dealt with are the felspars, 

 quartz, fluorspar, borax, cryolite, the alkalies, and 

 the various agents for colouring and for giving 

 opacity. The composition and properties of each 

 are given at some length, and the nature of the 

 impurities liable to be present and their effects 

 on the character of the enamels are clearly set 

 forth. 



A point of practical importance is emphasised 

 as regards the felspars that, as a rule, it is in- 

 advisable to replace felspar silica by quartz or 

 clay, even although the equivalent proportions are 

 observed. In this connection it is well known that 

 in enamels, as in many other substances, identity 

 in chemical comjxjsition is often accompanied by 

 considerable divergence in physical properties. 



The author has evidently had considerable prac- 

 tical experience in enamelling, and the remarks 

 appended to the description of each of the 

 materials on their role and application in works' 



