August 30, 19 17] 



NATURE 



523 



TWO BOOKS OX MIXER ALS. 



(j) A Pocket Handbook of Minerals, Designed 

 tor Use in the Field or Classroom, with Little 

 Reference to Chemical Tests. By Prof. G. 

 Montague Butler. Second edition. Pp. ix + 

 311 -f table in 5 folding- sheets. (New York: 

 John Wiley and Sons, Inc. ; London : Chapman 

 and Hall, Ltd., n.d.) Price 115. 6d. net. 



(2) Microscopical Determination of tJie Opaque 

 Minerals: An Aid to the Study of Ores. 

 By Dr. J. Murdoch. Pp. vii -f 165. (New- 

 York : John \\'iley and Sons, Inc. ; London : 

 Chapman and Hall, Ltd., 1916.) Price 95. 6d. 

 net. 



'T'HESE two books form a useful addition to the 

 -*- already large number of American publica- 

 tions on determinative mineralogy. 



(i) Prof. Butler's volume, now in its second 

 edition, is specially designed for use in the field, 

 and can easily be carried in the coat-pocket. A 

 brief account is given of each mineral, and there 

 is a useful table of the most characteristic prop)er- 

 tles of the different species, so that the recog- 

 nition of a specimen should as a rule present little 

 difficulty. The table does not, however, include 

 specific gravity, one of the most generally useful 

 means of identification. Even in the field a 

 ^Valker's balance, or for smaller specimens the 

 simple arm' balance employed by Penfield, is avail- 

 able. The work appears on the whole to have 

 been well done, though in a book containing so 

 much detailed information there are naturally 

 some points open to criticism. Oligoclase is 

 described quite correctly as AbeAn — Ab^An, but 

 a note is added that Ab = Na:O.Al,03.6Si02 and 

 An=:CaO.Al203.2SiO;. This is misleading, for 

 according to general usage Ab only represents 

 half the amount of albite indicated by the former 

 formula. Garnierite is not now the most im- 

 portant ore of nickel. The "compact fibrous 

 masses " of crocidolite (blue asbestos) resemble in 

 structure, not ordinary amphibole asbestos, but 

 serpentine asbestos (chrysotile, better referred to 

 by its older name, karystiolite). Again, it is not 

 much use giving the value of precious stones per 

 carat without specifying the size. 



(2) Dr. Murdoch's book, on the other hand, is 

 intended as a guide to students who wish to studv 

 the structure and composition of the opaque 

 metallic ores in the laboratory, by examining- the 

 pK>lished surface under the microscope. There 

 IS a useful introduction describing the methods 

 employed and the results that can be obtained, 

 followed by tables for identification. The first 

 classification is by colour, the next by hardness, 

 and the third by the behaviour with reagents. 

 Konigsberger's earlier method of observing 

 the optical characters of opaque minerals in 

 polarised light is described, but not his later 

 method {Centralhlatt fur Min., etc., 1909, 

 p. 245), which promises to be of more general 

 utilitv. 



J. W. E. 

 NO. 2496, VOL. 99I 



OUR BOOKSHELF. 



A Manual of Field Astronomy. By Andrew H. 



Holt. Pp. X4-I28. (New York: John Wiley 



and Sons, Inc. ; London : Chapman and Hall, 



Ltd., 191 7.) Price 65. net. 



This is a handy and lucid manual dealing with 



all the problems that arise ift field work with a 



j theodolite, namely, determinations of altitude, 

 latitude, azimuth, time, and longitude. It con- 

 tains a useful list of formulae for obtaining any 

 element of the astronomical triangle in w hich three 

 elements are supposed to be known. Attention 

 may be directed to the unusual notation ; the polar 

 distance, zenith distance, and colatitude are called 

 z, p, and s respectively ; this is because they 

 are oppMDsite the points Z, the zenith, P, the pole, 

 and S, the star. The explanations refer through- 

 out to the American Ephemeris, but the arrange- 

 ment of the British Nautical Almanac is so similar 

 that they will ser\-e equally for it. All needful 

 corrections, such as parallax and refraction, are 

 explained, but the author deliberately refrains from 

 introducing refinements that are of no imp>ortance 



I for work in the field. It is evident from a study 



' of the examples that the degree of accuracy con- 

 templated by the author is only of the order of the 

 nearest 10". A considerably higher degree of 

 accuracy is attainable with field instruments of the 

 finest type, but the methods explained in the book 

 will suffice, if carefully followed, to give this 

 greater refinement. 



An appendix explains the use of the "solar 

 attachment," which is designed to solve the 

 astronomical triangle mechanically, and give a 

 direct determination of the meridian from an 

 observation of the sun at any time. The accuracy 



I attainable with it is stated to be not much greater 

 than the nearest minute of arc. ' 



AxDREW C. D. Crommelin. 



Stanford's Half-inch Map of the Battle Front in 

 France and Flanders: Ostend, Zeehrugge, 

 Bruges. War Map No. 23. (London: E. Stan- 

 ford, Ltd., 1917.) Price 25. 6d. 

 This sheet is a continuation northward of the 

 map of the British battle front in France and 

 Flanders previously published by the same firm. 

 It extends from Dunkirk in the west to within 

 six miles of Flushing in the east, and southward 

 to the latitude of Roulers, and so comprises the 

 srreater part of the plain of Flanders. There is 

 little high ground in this region, and the only 

 contour shown is that of 125 ft. All the ground 

 above that height is stippled light red. The 

 method is successful so far as this sheet goes 

 but on higher srround done on a uniform method 

 the depth of colour would obscure the map. There 

 are no sf)ot heights, but they are scarcely re- 

 quired in Flanders. Woods, lakes, and marshes 

 are shown by conventional signs w-ithout colour- 

 ing. Roads, railways, and canals are clearlv 

 marked. As regards roads, apparently there is 

 a differentiation into main-roads, by-roads, and 

 ; tracks. This, however, is not stated in the ex- 



