662 



SCIENCE 



[N. S. Vol. XXVI. No. 672 



surface, wliere solidly frozen, practically no 

 erosion of rock surfaces takes place. 



The wind carries away the dust of dis- 

 integration; loose stones are often smoothed 

 and pitted by the sand blast, as in desert re- 

 gions; and some of the harder surfaces re- 

 ceive a superficial glaze. Wind carries away 

 the smaller rock fragments, and, on rare 

 occasions, the sudden outbursts of short-lived 

 glacial torrents spreads mud and sand over 

 the surface of floating glacier ice. 



Sulphate and chloride of sodium occur on 

 the floating ice, partly as concentrates or exu- 

 dates from freezing sea water, sometimes in 

 mounds several feet across and as much as two 

 feet thick. 



In a general way the ice must he regarded as 

 at present retreating, though the amount of 

 retreat is moderate. The rocks in their 

 petrologic aspect are thoroughly discussed by 

 Dr. Prior. 



The text of the volume is replete with ex- 

 cellent half-tone cuts from photographs, and 

 to the plates are added two well-executed 

 charts. Wm. H. Dall 



Clean Water and How to Get It. By Allen 

 Hazen. New York, John Wiley & Sons. 

 Nothing could be more timely than a book 

 dealing with the subject of water supply, for 

 all over the country there is a remarkable 

 awakening of interest in improvements along 

 this line. High death rates from typhoid 

 fever in American cities have too long been 

 a reproach to our civilization and the inaction 

 which has permitted them is rapidly giving 

 way to a wholesome spirit of reform. No one 

 is better fitted to meet the need for popular 

 treatment of this subject than Mr. Allen 

 Hazen, whose own engineering skill has con- 

 tributed ^o largely to develop the newer 

 methods of water purification. This book is, 

 therefore, a doubly welcome one. 



The popularization of the results of scien- 

 tific investigation is a difficult task. On the 

 one hand is a mass of fresh information which 

 needs only popular education to make it 

 effective in practise; on the other hand is a 

 large and intelligent public waiting for the 

 information which it would gladly apply. 



The intermediary is still too often lacking 

 because the qualities of scientific grasp and 

 popular exposition are so rarely joined. On 

 one side lies the pitfall of patronizing over- 

 simplicity into which certain well-known au- 

 thorities have recently so notably fallen. On 

 the other side is the danger of being too 

 technical, lacking in the clear analysis and 

 telling exposition necessary to appeal to the 

 untrained mind; this, if anything, is Mr. 

 Hazen's error. His book is designed, as he 

 states, especially for public officials who have 

 been drawn from walks of life in which they 

 have had no water-works experience and who 

 wish to serve their cities well and can perhaps 

 be aided in doing so by very simple statements 

 as to certain matters. He modestly disclaims 

 any intention of helping members of water 

 boards and water-works superintendents, whom 

 he believes to be familiar with the informa- 

 tion which he gives. If the reviewer is not 

 mistaken, however, the book will prove of very 

 great value to the latter class of readers and 

 will reach only exceptional individuals among 

 the former. In a new edition, which is sure 

 to be called for soon, the path to the solid 

 knowledge the book contains might be made 

 easier by a more logical arrangement of its 

 contents and by the addition of two ele- 

 mentary chapters, one outlining, at the begin- 

 ning of the book, the general characteristics 

 of a good water-supply, and one, in the middle 

 of the book, on the general plan and principles 

 of water filtration. 



In the present work the author begins 

 with a detailed description of certain sur- 

 face supplies. Then follows, in the next suc- 

 ceeding chapters, an admirable review of vari- 

 ous sources of water supply, in which the 

 grasp of trans-Atlantic conditions made pos- 

 sible by the writer's wide experience is tellingly 

 evident. He discusses the use of large lakes 

 for water supply and shows why Milwaukee 

 and Duluth are comparatively free from 

 water-borne typhoid, while Chicago and Cleve- 

 land have suffered so heavily. River waters 

 are next discussed, and the ground is wisely 

 taken that a certain amount of bacterial pollu- 

 tion is a necessary characteristic of surface 

 waters and that the responsibility for the re- 



