Chemistry and Physics. 95 



as in the method of mixtures at a mean temperature between that 

 of the heated and of the cooled gas. 



In the experiments as carried out, direct measurements were 

 made of the time taken by a sound wave to travel a known dis- 

 tance through the gas which was contained in a coiled tube so 

 that it could be raised to the desired temperature. Each end of 

 the tube was closed by a steel diaphragm which might be struck 

 by a hammer controlled by an electromagnet. As the compres- 

 sion travelled along the tube it successively raised two disks 

 placed about 18 meters apart, breaking a circuit, and recording 

 the interval of time elapsed upon a pendulum chronograph. As 

 certain small portions of the tube at either end projected beyond 

 the bath, or furnace, and were cooled by a water jacket, it was 

 necessary to introduce a proper correction for these ends. 



The different gases studied were air, nitrogen, carbon dioxide, 

 nitrous oxide, methane, ethane and argon. Tubes of lead, steel 

 and silica were employed. The lead tube was conveniently used 

 for temperatures up to 100° C. and the steel tube for the higher 

 temperatures up to 1000° C. Exception had to be made however 

 in the case of air and carbon dioxide as they attacked the metal. 

 For these gases a tube of silica heated electrically by a wire coiled 

 around it was employed. The relation between the velocity of 

 sound in a tube and that in a free gas is discussed and a satis- 

 factory correction formula adopted. 



The means of the velocities as found from the different tubes 

 were then plotted and tabulated for the different temperatures 

 and the various gases. The formulas both for the ratio of the 

 specific heats and their difference are introduced and the values 

 calculated. The final result sought, namely, the value of the 

 specific heat expressed as a function of the temperature is now 

 calculated, and discussed with reference to the determinations of 

 other investigators. For the detailed results the reader will 

 desire to consult the original memoir. — Proc. Boy. Soc. 100, 1, 

 1921. F. E. B. 



8. Traite de Dynamique; bv Jean D'Alembert. Vol. I, pp. 

 XL, 102. Vol. II, Pp. 187. Paris, 1921 ( Gauthier-Villars et 

 Cie) . This is a reprint in the collection, Les Maitres de la Pensee 

 Scientifique, of the work of D'Alembert edited by Maurice Sol- 

 orine. As these memoirs are most complete they may, in the 

 words of the editor's notice, be regarded as indispensable docu- 

 ments to historians of science and civilization. They also offer to 

 the student an easy and inexpensive means of meeting at the 

 source the experimental methods and ingenious processes of the 

 great investigators. To many these concrete methods will be far 

 more fertile and suggestive than the schematic rules of the 

 manuals. f. e. b. 



9. Heat and Light; by S. E. Brown. Pp. numbered 170- 



