July r, 1922] 



NA TURE 



no doubt that nothing is so inspiring and fascinating 

 as the perusal of the account of a great discovery by 

 the discoverer himself. The personal element, so con- 

 spicuously absent in current textbooks, is in this way 

 given its opportunity, especially if the discoverer's 

 account is read in the original language in which it 

 was written. The series now being issued under the 

 editorship of M. Solovine is therefore to be welcomed. 



The present essay was first printed as an introduction 

 to Laplace's " Theorie analytique des probabilit.es." 

 It gives in non-mathematical language the principles 

 underlying Laplace's methods for dealing with the 

 theory of probability, and shows how it is applied to 

 problems of natural science — especially the astro- 

 nomical problems to which Laplace applied his 

 genius — to sociology and other aspects of Gommunal 

 life. Special attention is devoted to errors in the 

 estimation of probabilities, due to psychological causes, 

 and there is also a brief history of the methods of 

 probability. 



Considerable modification has since been introduced 

 into the fundamental notion of probability, but Laplace's 

 essay should be read by all students of mathematics. 

 In it occurs the sentence : " Une intelligence qui pour 

 un instant donne connaitrait toutes les forces dont la 

 nature est animee et la situation respective des etres 

 qui la composent, si d'ailleurs elle etait assez vaste 

 pour soumettre ces donnees a l'analyse, embrasserait 

 dans la meme formule les mouvements des plus grands 

 corps de l'univers et ceux du plus leger atome : rien 

 ne serait incertain pour elle, et l'avenir comme le passe 

 serait present a ses yeux." S. Brodetsky. 



Displacement Interferometry applied to Acoustics and to 

 Gravitation. By Prof. Carl Barus. Pp. viii+149. 

 Publication 310. (Washington : Smithsonian Insti- 

 tution of Washington, 1921.) 

 Prof. Barus' work is divided into twelve chapters, 

 and occupies an intermediate position between the usual 

 textbook dealing with routine work and the ordinarv 

 type of original research which attacks and solves some 

 specific and definite problem. It is throughout of an 

 exploring nature and may be said to investigate the 

 suitability of interferometry as a method for research 

 in various branches of acoustics and gravitation. In 

 the first chapter the open mercury manometer, when 

 read by interference, is discussed. In the second, the 

 inteiferometer U-tube is used as an absolute electro- 

 meter. The third deals with acoustic pressures, the 

 fifth treats of the compression of a sound wave in a 

 pipe, and the sixth with the vibration of a telephone 

 plate. In the eighth and following chapters various 

 gravitational problems are approached. The book is 

 a storehouse of unusual experimental methods and 

 may be consulted with advantage by any one about 

 to commence investigations along the lines indicated. 



Publications of the Washburn Observatory of the Univer- 

 sity of Wisconsin. Vol. X. Part 4 : Observations of 

 Double Stars, 1907-1919. By George C. Comstock. 

 Pp. 167. (Madison. Wis. : Washburn Observatorv, 

 n.d.) 

 The volume under notice forms a catalogue of all 

 the observations of double stars made with the 16-inch 

 refractoi at Washburn Observatory by Prof. Comstock 



NO. 2748, VOL. I io] 



between 1907 and 1919 ; summaries of his earlier 

 observations with the same instrument from 1889 to 

 1907 are also given, so that it is possible to detect 

 changes. There are some 200 stars in the catalogue, 

 including most of the well-known binaries. 



The probable errors are given as 2°-6, o"-o3 for 

 separations less than o"-5, and o°9, o"-o7 for those 

 between 2" and 4". Wires illuminated by red light 

 were employed. This involves the possibility of small 

 errors through unequal refraction of the images of wire 

 and star in the eyepiece, unless the latter is achromatic. 

 A list is given of the eyepieces, which are either Rams- 

 den or Kellner, with powers varying from 196 to 1540 ; 

 about 800 was commonly used. A. C. D. C. 



Drugs in Commerce : Their Source, Preparation for the 

 Market, and Description. By J. Humphrey. (Pit- 

 man's Common Commodities and Industries.) Pp. 

 xi + 116. (London: Sir Isaac Pitman and Sons, 

 Ltd., n.d.) 35-. net. 

 Mr. Humphrey has contrived to include within the 

 moderate compass of 113 pages of text a good 

 account of the drugs of natural origin found in com- 

 merce. The information given includes descriptions 

 of the drugs, notes on their constituents and sources 

 of supply, and in most cases some particulars as to 

 their modes of preparation for the market. Great 

 pains have evidently been taken to secure accuracy, 

 but it should have been pointed out that the " hen- 

 bane " imported from Egypt is not derived from 

 Hyoscyamus niger. 



The book contains six plates illustrating the more 

 important drugs, e.g. cinchona, ergot, opium, and 

 jaborandi, and six more showing scenes in drug ware- 

 houses at the London Docks and methods of packing 

 and selecting the spices, such as nutmeg and cinnamon, 

 used in medicine. The book can be cordially re- 

 commended to any one desirous of obtaining general 

 information regarding this interesting and little-known 

 group of commercial products. 



Memoirs of the Geological Survey : England and Wales. 

 The Water Supply of Cambridgeshire, Huntingdon- 

 shire, and Rutland from Underground Sources. By 

 W. Whitaker. Pp. iv+157. (Southampton: Ord- 

 nance Survey Office ; London : E. Stanford, Ltd., 

 11)^2.) 75. net. 

 The latest addition to the series on the underground 

 water supplies of England deals with three counties 

 which form a convenient unit. The counties being agri- 

 cultural rather than industrial or manufacturing, very 

 large water supplies are required in few cases. Supplies 

 are obtained chiefly by means of wells, but some water 

 is obtained from springs, notably the supply of the 

 town of Wisbech, which, however, obtains its water 

 from the county of Norfolk. At least one town of more 

 than 5000 inhabitants seems to have no public supply. 

 Chalk and, to a less extent, lower greensand are the 

 sources of water in these counties. The Oolites and 

 Lias are also of some importance. The value of 

 chalk in this respect in the south-east of England 

 corresponds with that of New Red sandstone in the 

 Midlands. In addition to full details of the wells 

 and springs in the three counties Mr. Whitaker gives 

 some useful indications as regards enlarging and im- 

 proving existing supplies. 



