XII. SPECIAL COLLECTIONS. 335 



1748. Apparatus, by A. de la Rive, for the derivation and 

 the relative measurement of Induced Currents. Used by 

 himself in his studies upon rarefied gases. 



De la Rive Collection. The property of Messrs. Soret, 

 Perrot, fy Sarasin, Geneva. 



Used for diverting into a galvanometer a very small portion of a current of 

 induction. This current passes through a glass trough filled with distilled 

 water, in which are dipped two platinum wires, joined to the galvanometer. 

 The current which was passing through the thin liquid thread placed between 

 the wires is partially diverted into the galvanometer, which thus measures a 

 quantity proportioned to the total intensity of the induced current that may 

 go through the trough. 



The deviation of the needle of the galvanometer increases proportionally 

 with the distance between the wires. 



This apparatus was often used by De la Rive in his researches respecting 

 the passage of the induced current through rarefied gases. 



1748a. Apparatus used by De la Rive and Sarasin to de- 

 monstrate that Rarefied Gases, crossed by inductive discharge, 

 become condensed under the action of magnetism. 



De la Rive Collection. The property of Messrs. Soret, 

 Perrot, fy Sarasin, Geneva. 



The inductive current passing through the tube with two compartments, 

 one of which is placed between the two poles of a powerful electro-magnet, 

 the glass cock is rapidly turned round, thus interrupting the current, and 

 separating the two compartments. These are afterwards brought into com- 

 munication with a very sensitive manometer, and it is then found that the 

 pressure is a little greater in the one which has been between the two poles of 

 the magnet, and which will also contain the negative electrode. 



(See Archives des Sciences Physiques et Naturelles ; new period, vol. 41, 

 p. 5 ; and Philosophical Magazine, 4th series, vol. 42, p. 211.) 



1748b. Apparatus used by A. De la Rive in his Studies upon 



the Magnetic Rotatory Polarisation of Liquids. (Made 



by the Geneva Association for Constructing Scientific Instruments.) 



De la Hive Collection. The property of Messrs. Soret, 



Perrot, fy Sarasin, Geneva. 



1. The Nicol polariser. 



2. Tube for holding liquids, Avith double wrapper for the heating required 

 for studying the influence of the atmosphere upon the phenomenon. 



3. The Analyser, with graduated circle and special register, hi vented by 

 M. Thury. This consists of two tangent discs in ivory, the one supported 

 by the analysing JNicol, the other by the pinion that helps to turn it, and of a 

 horizontal ruler. A pencil mark made by this ruler on both discs shows the 

 position of the Analyser. Instead of having to read each observation sepa- 

 rately, which is inconvenient in experiments made in the dark, the corre- 

 sponding mark to every observation is simply noted, and afterwards reckoned 

 altogether. (See Archives des Sciences Physiques et Naturelles, vol, 38, 

 p. 209.) 



1749. Apparatus designed by Auguste de la Rive, for the 

 demonstration of the Electric Theory of the Aurora Borealis. 



