80 Mr. F. T. Trouton on the Influence of 



The apparatus has been applied to the comparison of the 

 compressibility of solutions with that of the solvents, and the 

 results exhibit the same general relations as with other 

 properties of solutions. The solutions divide themselves into 

 two classes, which may be broadly termed electrolytic and 

 non-electrolytic. In the first there is a very considerable 

 decrease in compressibility, as much as 8 per cent, with a 

 3-per-cent. solution of NaCl ; whilst in the second there is 

 but a slight diminution, quite beyond the limits of accuracy 

 of the apparatus. For instance, a 5-per-cent. solution of 

 naphthalene has a diminution of under 1 per cent. 



A strict interpretation of the theory of osmotic pressure in 

 solutions has been made by Prof. J. J. Thomson, in his 

 " Applications of Dynamics to Physics and Chemistry," § 97, 

 where he finds that 1 gram-equivalent per litre would decrease 

 the compressibility by 1 part in a thousand. Non-electrolytes 

 in dilute solution appear to follow this law ; this is in agree- 

 ment with their other properties, such as alteration in boiling- 

 or freezing-points. 



The diagram will serve to explain the general arrangement 

 of the apparatus. 



' XIV. The Influence the Size of the Reflector exerts in 

 "Hertz's Experiment." By Feed. T. Trouton*. 



OWING to the requirements of certain refraction experi- 

 ments in which I was engaged, it became necessary to 

 investigate more fully than had been previously done f the 

 influence the size of the reflector has in determining the 

 position of the nodes in Hertz's now well-known electro- 

 magnetic interference experiment. 



Kadiation of a suitable period was produced by Hertz for 

 this experiment, as is well known, by taking advantage of the 

 alternating character of the discharge of an electric condenser. 

 For this purpose two similar conductors, generally speaking- 

 two brass cylinders, are placed together end to end with a 

 spark-gap between them, and are charged by an induction- 

 coil, with the poles of which they are connected. The rapidly 

 alternating current which occurs between them at each dis- 

 charge originates electromagnetic waves which spread out 

 into space. In these waves the electric component is parallel 

 to the common axis of the cylinders, while the magnetic com- 

 ponent lies at right angles. 



* Communicated by the Author. 



t ' Nature/ Aug. 22nd, 1889. 



