July 13, 1905] 



NA TURE 



243 



A short history is given in chapter viii. of the 

 general development of triangulation from the time 

 of Snellins to the present day, but it consists mainly 

 in mentioning some of the more striking incidents 

 connected with the subject, such, for instance, as the 

 use of electric light in the work connecting Spain and 

 Algiers. 



The question of lateral refraction is gone very fully 

 into, and a table is given showing the mean triangular 

 errors proportional to triangles of different sizes. The 

 deduction is then made that the effect of lateral re- 

 fraction increases with the mean length of a side of 

 a triangle up to about 90 kilometres, after which it 

 begins to decrease again. This is a particularly 

 interesting problem, and the table, which is taken 

 from a recent triangulation in Germany, certainly 

 confirms the deduction. It is of course assumed that 

 the closing errors of triangles are due in most part to 

 lateral refraction. The usual methods of calculating 

 and computing triangulation are very thoroughly 

 dealt with. 



Precise levelling forms the greater part of 

 chapter ix., but an exceedingly full and clear demon- 

 stration is given at the beginning of the various 

 formula relative to atmospheric refraction and to 

 trigonometrical differences in heights of stations. 

 This is treated in a really very clear manner. 



Three chapters are devoted to the theory of prob- 

 ability and its application to geodesy. The theoretical 

 portion has been well demonstrated, and differs but 

 little from the numerous text-books on this subject; 

 but where the attempt is made to apply the method 

 of least squares to a network of triangulation, the 

 want of taking a practical example is at once felt. 

 Clarke, in his " Geodesy," gives numerous examples 

 of how to apply theory to practice, but Signer 

 Pizzetti leaves the student utterly in the dark on this 

 important point. 



Perhaps the two most interesting chapters are left 

 to the end. They deal with the subject of projections, 

 which is gone into with every care. There is scarcely 

 any well known projection which is not very fully 

 explained. 



Altogether this book is a distinct addition to any 

 geodetic library. W. J. Johnston. 



OVR BOOK SHELF. 

 The Food Inspector's Handbook. By Francis 



\'acher. Fourth edition. Pp. xvi + 231; illustrated. 



(London : The Sanitary Publishing Co., 1905.) 



Price 3^. 6d. net. 

 This is a pocket volume intended for the use of 

 sanitary and other officers concerned in the inspec- 

 tion of food. It describes, in simple, untechnical 

 language, the naked-eye characters of the various 

 foodstuffs met with in ordinary commerce, and points 

 out the physical signs by which unwholesome food 

 may be detected. 



The first sixty pages deal chiefly with the statutory 

 powers by virtue of which the food-supply of the 

 community is supervised. They include a summary, 

 with explanatory comments, of the various enactments 

 — Public Health Act, Sale of Food and Drugs Acts, 

 and so on — bearing upon the control of food from the 

 inspector's point of view. Next follow chapters treat- 



NO. 1863, VOL. 72] 



ing of meat, poultry, and fish. This is the most 

 important part of the book, and the notes upon the 

 ante- and post-mortem signs of those diseases which 

 render flesh-food unfit for consumption, or which 

 seriously depreciate its quality, will be especially 

 valuable to sanitary officers who have had no 

 veterinary experience. A subsequent chapter is 

 allotted to fruit and vegetables, and one to milk ; 

 the rest of the book gives short descriptions of cereals, 

 dairy products, tea, sugar, spices, and so forth. This 

 section, though of interest to the food inspector, is 

 of less concern to him than the foregoing, the quality 

 of the articles mentioned being generally .a matter 

 for decision by analvsis, not for condemnation at 

 sight. 



The author gives sensible advice, and his little 

 volume should be found very useful to those for whom 

 it is written. The only inaccuracy we have noted is 

 suggested in the statement that " Dutch cheese is 

 below the standard per cent, as regards fat"; this 

 might imply that there is a legal standard, which is 

 not the fact. C. S. 



Maniiale deW'lngegnere Elettricisia. By Attilio 



Marro. Pp. xv+689. (Milan: Ulrico Hoepli, 



iqo5.) Price 7.50 lire. 

 This book forms one of the useful series of " Manual! 

 Hoepli," which already comprises over 800 distinct 

 treatises. Its aim is to give to engineers and elec- 

 trical constructors most of the information and data 

 that they are likely to require in practice. On this 

 account it is not so much a text-book as a -classified 

 collection of rules and data ; but on account of its 

 containing a large amount of explanatory matter it 

 lies intermediate between a treatise on electrical 

 engineering and a pocket book of electrical rules and 

 tables. The type being small but clear, a very large 

 amount of useful information is collected in a small 

 compass. The numerical data have been obtained 

 principallv from recent papers published in the 

 journals of electrical engineering, and are collected 

 in 115 tables. The work is illustrated with 192 cuts 

 and is furnished with a good index. Its size well 

 adapts it to be a handy pocket book of reference, and 

 it is likely to prove of considerable use. 



Poisonous Plants of all Countries. By A. B. Smith. 



Pp. xvi + 88. (Bristol: J. Wright and Co., 1905.) 



Price 2S. 6d. net. 

 The author has collected a fairly representative list 

 of poisonous plants, which he has arranged according 

 to the action produced and the organs affected, but 

 there is no mention made of the part or parts of the 

 plant which furnish the poison. The descriptions, 

 which form the main part of the text, are sufficient 

 where reference is made to the whole plant, but the 

 majority are too meagre to be diagnostic. The 

 string of vernacular names which is quoted in several 

 cases does not serve any useful purpose, whereas 

 beyond the mere name of the toxic principle inform- 

 ation which is much required is not given. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 ,Vo notice is taken of annnynwns communications.] 

 The Constant of Radiation as Calculated from 

 Molecular Data. 

 In Nature, May iS, I gave a calculation of the 

 coefficient of complete radiation at a given absolute tem- 

 perature for waves of great length on principles laid down 

 in 1900, and it appeared that the result was eight times 



