NA TURE 



[September 28, 1905 



the " sun-powers " of the various stars being repre- 

 sented by a system of symbols. Fig. 3 similarly 

 treats all those stars within 4S0 light-years, a map 

 of N.W. Europe constituting the background. The 

 scale employed for the stellar distances is an interest- 

 ing one, which takes as its unit the distance of a star 

 situated at one light-year from the solar system. 

 Mr. Heath fortuitously discovered that by calling this 

 unit one mile the sun's distance is almost exactly 

 represented by one inch. 



Figs. 4 and 5, of which detachable duplicates are 

 given in the book, present really beautiful pictures 

 when used with a stereoscope, the star images stand- 

 ing out in numerous planes, some quite near to the 

 eye, others apparently infinitely remote. The concep- 

 tion of the three-dimension character of space is most 

 vividly impressed by these charts, the first of which 

 represents the stars as viewed from a plane situated 

 500 light-years from the sun by eyes 107 light-vears 

 apart, the second a similar view at a distance of 100 

 light-years as seen by eyes 26 light-years apart. 



The sun-powers of various stars are more especially 

 dealt with in Figs. 6 and 7 and the accompanying 

 text, whilst Fig. 8 represents a view of the known 

 universe as it would appear to an external observer 

 looking in the direction of R.A. 6h. 



All the data (e.g. parallaxes, spectral types, sun- 

 powers) used in constructing the various diagrams 

 and discussed in the text, are given in tables which 

 form an interesting and useful appendix to the 

 volume. Avowedly written in a popular form, the 

 book contains much that will not appeal to the 

 astronomer, e.g. the reference to the Dogger Bank 

 incident on p. 17, but should prove of interest and 

 assistance to the amateur tourist in space by visual- 

 ising the real interpretation of stellar parallaxes. 



In the second of these two volumes Mr. Heath 

 gives us a series of six stereoscopic charts of the sun 

 and stars of which the parallax has been determined, 

 similar to those mentioned above. The scale of the 

 charts here given is one-fifth of that he employed for 

 his large stereoscope, and in all of them the spec- 

 tator's eyes are supposed to be 26 light-years apart, 

 each drawing being made at any angular distance 

 of go degrees from the four adjacent to it. Each 

 view is accompanied by a table similar to those 

 mentioned above. 



The idea of representing stars in this stereographic 

 manner is very ingenious, and this book, too, will 

 certainly interest many astronomical readers. 



PHYSICAL CHANGES IN IRON AND STEEL. 

 The Crystallisation of Iron and Steel. An Introduc- 

 tion to the Study of Metallography. By Dr. J. W. 

 Mellor. Pp. X+144. (London: Longmans, Green 

 and Co., 1905.) Price 55. net. 

 'T'H.AT the students of the problems of metal- 

 -•- lography, particularly in the present unsettled 

 state of affairs, should have for guides only 

 those who have done some considerable amount 

 of active work in the science will be readily 

 acknowledged. A certain amount of familiarity 

 with the metals themselves, their history and 

 NO. 1874, VOL. 72] 



behaviour, is also necessary before the subject can 

 be made to live. Reading through the present 

 work convinces one that it is written by an onlooker, 

 and the illustrations entirely support this view of 

 the text. The presentation is without bias, and 

 each theory and method is described and examined 

 as clearly and fairly as the author's evident lack of 

 practical acquaintance with the subject as a whole 

 will permit. For anyone wishing to get an idea of 

 what has been done and desiring a general survey of 

 the scope of metallography, its theoretical aspect, and 

 the problems it endeavours to solve, the book will 

 serve fairly well. For the worker actualh' in the 

 field, striving to progress in the science, to applv it 

 to his own practical work with metals, and perhaps 

 to endeavour by its aid to solve some of the difficul- 

 ties that are ever confronting the metallurgist, it can- 

 not honestly be recommended, as to such it will give 

 but little light. 



A few examples of the kind of thing encountered 

 may be given. On p. 12, the recalescence curve of 

 steel is shown as rising from 680° C. to about Sio° C, 

 whereas the real rise is only a few degrees ; p. 14, 

 " Ac2 is higher than Ar2 "; p. 49, " excess of ferrite 

 renders the steel ductile and tenacious," whereas pure 

 iron has a tenacity of about 20 tons and pure pearlite 

 of over 50 tons per square inch; p. 50, " 2 per cent, 

 carbon alloys are called cast iron " is quite wrong, 

 for tons of steel are made with more than 2 per cent, 

 carbon. Malleability is the essential point here. 

 P. 52, discussing the influences which affect the 

 physical properties, the author omits mechanical 

 treatment— hot or cold work. " Heat white cast iron 

 it forms grey cast iron " is quite misleading. P. 74, ii., 

 is erroneous, and p. 76 is not in accord with 

 the facts, as the writer has many times proved even 

 in ordinary works practice, so there is only left the 

 ingenuity of the explanation and the fact that it lead> 

 the reader astray. P. 81, "tenacity is lowered b\ 

 silicon." .\re the researches of Hadfield, Arnold, and 

 Baker not sufficient to the contrary? Their results 

 are not disputed. On p. 88, cleavage fragments are 

 laboriously dealt with as crystallites. The reader is 

 told they are perfect replicas of the larger crystal, and 

 calcite is the example chosen I Sorby's samples are 

 said to be i square cm. by 2 mm. thick. The 

 originals are in front of the writer, and their surface 

 area is more than i square inch. It may be of little 

 importance, but the statement should either be near 

 the truth or be omitted. P. 106, " the cheapest 

 microscope, 16I. or upwards," and " it is necessary 

 to have a brilliant light arc lamp, &c.," must dis- 

 courage many isolated students, whereas much excel- 

 lent work has been done and is being done with a 

 batswing or a similar burner and a Beck's Star 

 set at about 7/. P. 107, " microphotography. " 



A glossary gives the " nomenclature of metallo- 

 graphy," and the present reviewer would like to 

 study the faces of his colleagues of the Iron and Steel 

 Institute's Committee on "The Nomenclature of 

 Metallography " when they find that it is not based 

 on the final report, but on the crude original put out 

 expressly for discussion and amendment. The 

 arduous session's work that followed was evidcntlv 



