378 Notices respecting JSew Books. 



known, small quantities of dissolved substances lower the 

 surface-tension. On shaking with air we have the two 

 opposite actions — increase of surface-tension due to breaking 

 up of the cells and decrease of surface-tension due to solution 

 of air, the latter being the greater. 



Hence the three colloids experimented upon all behave as 

 non-homogeneous liquids, showing only differences of degree. 

 In each case the viscosity at any temperature is not a constant 

 quantity but depends on the size of the contact surface of 

 the two constituents. The logarithmic decrement of a disk 

 oscillating in the solution in each case depends upon the size 

 of the amplitude. The observed differences point to the gela- 

 tine cell-walls being thinner than 2L while those of silicic acid 

 and albumen are thicker than 2l. 



XL VIII. JSotices respecting New Books. 



La Telegrafia Senza Filo. Di AuGrsTo EiGHi e Beexardo Dessau. 

 Con 259 figure intercalate uel teste. Bologna : Ditta Xicola 

 ZanicheUi. 1903. Pp. viii + 518. 



^PHE authors of this work inform us in their preface that their 

 -*- book is not intended to be a scientific treatise on wireless tele- 

 graphy. This statement must, however, be accepted as true in a 

 limited sense only — the work is strictly non-mathematical, and from 

 beginning to end we have not come across a single mathematical sym- 

 bol or equation. But in another sense tlie work is, though popular, 

 yet truly scientific — the results of the recent remarkable develop- 

 ments of electrical theory being carefully and lucidly ex])lained. 

 There is none of that looseness of language and misleading vagueness 

 which are only too often associated with so-called popular books 

 on scientific subjects. Any person possessing a knowledge of 

 elementary physics should find the volume delightful reading ; 

 while the more adAanced student will find numerous references to 

 original sources of information. 



The work is divided into four parts. Part I. deals with electrical 

 phenomena generally, including electrostatics, electric currents, the 

 electromagnetic field, and what is practically a verbal statement 

 of the equations of the electromagnetic field. Part II. is devoted 

 to electromagnetic waves : beginning with an account of the 

 oscillatory discharge of a condenser and Peddersen's experiments, 

 the authors lead up to Hertz's brilliant investigations, giving illus- 

 trated descriptions of the more important forms of oscillators and 

 resonators used by different experimenters, and a very complete 

 account of detectors of electromagnetic radiation. Part III. is the 

 most important section of the work, and contains a brief historical 

 sketch of the development of telegraphy, and a full account of the 



