XII. SPECIAL COLLECTIONS. 385 



1748. Apparatus, by A. De la Hive, for the derivation and 

 the relative measurement of Induced Currents, and used by 

 him in his studies upon rarefied gases. 



De la Rive Collection. The property of Mess-rs. Soref, 

 Perrot, fy Sarasin, Geneva. 



This was used for diverting into a galvanometer a very small portion of an 

 induction current, which passes through a glass trough filled with distilled 

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

 The current passing through the thin liquid thread placed between the wires 

 is partially diverted into the galvanometer, Avhich 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 on the 

 passage of the induced current through rarefied gases. 



17 48 a. Apparatus used by De la Hive 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, 

 Pcrrot, Sf Sarasin, Geneva. 



The induced current passes 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 Hive in his Studies upon 

 the Magnetic Rotatory Polarisation of Liquids. (Made 

 by the Geneva Association for the Construction of Scientific In- 

 struments.) 



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

 Perrot, $ Sarasin, Geneva. 



1. Nicol polariser. 



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

 for studying the influence of the temperature upon the phenomenon. 



3. Analyser, with graduated circle and special register, invented by M. 

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

 by the analysing Nicol, 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 read 

 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, 



40075. B b 



