REVIEWS 145 



into "topazite" and " turquoisite " respectively, especially as such forms 

 as " galenite " are adopted. 



In the second part of the book, an account of the methods of blowpipe 

 analysis is given. While this follows the usual lines, the descriptions, despite 

 their brevity, are clear, and form a useful introduction to the subject. The 

 only obvious omission is the general test for silicates ; the one which is 

 given in the book is applicable only to those silicates soluble in nitric acid. 



In order to be logical, the second and third sections should have preceded 

 the first, as it would be futile for a student to attempt to utilise the data 

 in the latter without, at least, a partial knowledge of the former. As a whole, 

 the book is curiously unequal, the first two sections being much better than 

 the third, which contains far more detail than is required, or is likely to be 

 attained, by the class of student for whom the book is intended. 



Misprints are rather numerous, while the errata slip which is inserted at 

 the beginning of the first part refers to the section on Crystallography. 



A. S. 



BOTANY AND AGRICULTURE 



Forests, Woods, and Trees in Relation to Hygiene. By Augustine Henry, 

 M.A., F.L.S. [Pp. xii + 314 with 28 photographic illustrations, 21 

 maps and plans, and i other figure in the text.] (London : Constable 

 & Co., 1919. Price 18s. net.) 



A LESS ambiguous title for this book would have been " The Afforestation 

 of Water-catchment Areas," for it is this subject that forms the writer's 

 main theme and occupies about three-quarters of the text. 



It is the introductory chapters which are more especially concerned 

 with the hygienic influences of forests, and these embrace an interesting 

 account of the afforestation of pit mounds, in which due credit is given 

 to the admirable work of the Midland Reafforesting Association, and a 

 rather too brief summary of the influence of forests on climate. 



Prof. Henry emphasises the importance of trees in affording shelter 

 from cold wet winds which reduce the vitality of plants and animals alike. 

 Quite rightly, too, the author lays stress on the psychical influence of trees, 

 an aspect too frequently lost sight of in estimating the value of different 

 environments in relation to health. The beneficial effect of trees in towns 

 is probably due much more to this cause than to either their shelter effect 

 or their action as a dust screen. 



In reference to the chief subject of these pages, the author has amassed 

 a large amount of statistical and other data, respecting the water-catch- 

 ment areas of Great Britain, which is set forth in detail. These gathering- 

 grounds number 266 and represent a total area of over 928,000 acres, of which 

 rather less than a fifth is actually owned by the towns concerned or public 

 companies. The universal acquisition, by the respective authorities, of 

 the entire catchment ground is strongly urged as a necessary preliminary 

 to the abolition of all habitations from such areas and their afforestation. 



A number of arguments are brought forward in support of this pohcy, 

 as, for example, the absence of pathogenic bacteria from woodland soils, 

 the reduced chances of pollution by flood water, and the diminution of 

 silting up of the reservoirs. It is also pointed out that the rainfall over 

 woodlands is higher than that over open country. In this connection, 

 however, it must be noted that the local augmenting effect of forest on 

 precipitation diminishes with the altitude, and, as Prof. Henry admits, only 

 the lower parts of the gathering-grounds could be profitably planted up. 



The area available for afforestation is estimated at from 10 per cent, to 

 70 per cent. , so that a combination of forestry and grazing would in most 

 cases be necessitated. 



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