XII. SPECIAL COLLECTIONS. 333 



1739. Diagrams of magnetic Curves, prepared by Faraday. 



Mrs. Faraday. 



1740. Coils and Helices, used by Faraday in his magneto- 

 electric researches. Mrs. Faraday. 



1741. Model frequently used by Faraday during his re- 

 searches on the rotation of a ray of polarized light by electricity 

 and magnetism. Mrs. Faraday. 



1742. Block of Glass pierced by sparks from an induction 

 coil. Presented to Faraday by M. Ruhmkorff. 1861. 



Mrs. Faraday. 



1742 a. Apparatus constructed by A. de la Rive for demon- 

 strating the rotatory motion which an electric discharge in rarefied 

 gas performs around a magnet. 



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

 Perrot, fy Sarasin, Geneva. 



This apparatus consists of an electric shell, perforated by a soft iron 

 cylinder, magnetised by placing it on one of the poles of an electro-magnet. 

 The electric discharge is produced between the extremity of the soft iron 

 cylinder, which is insulated by a glass tube, and a metallic ring which encircles 

 the soft iron. As soon as the soft iron is magnetised, the electric discharge 

 begins to revolve around it. Previous to Ruhmkorff's improvements in 

 induction-coils De la Rive made this experiment with the current of the 

 " Armstrong " machine. 



1742b. Original Apparatus, by Arago and Matteuci. 



Polytechnic School, Paris. 



1742c. Apparatus devised by De la Rive & Sarasin for 



demonstrating that the electric discharge in a rarefied gas, turning 

 under the power of a magnet, draws with it in its rotatory motion 

 the gas which tranmits it, and all bodies, sufficiently light, that it 

 meets with in its course. 



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

 Perrot, fy Sarasin, Geneva. 



A bell-glass stands upon a platten, which itself must be placed upon the 

 pole of an electro-magnet. This glass being filled with rarefied gas, the 

 electric discharge is completely effected between the central brass ball, and a 

 ring of the same metal constituting the other electrode. A sail- wheel is 

 adjusted inside this ring, so that its vertical paddles may be upon the direct 

 line from the ball to the ring, whereby the discharge strikes it in revolving 

 under the action of the magnet. It then gives it a rotatory direction as soon 

 as the direction of the magnet is changed. 



(See Archives des Sciences, vol. 45, p. 387; Philosophical Magazine, 

 vol. 44, p. 149.) 



1743. Induction Coil by Bonijol, an old Genevese maker. 

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



Perrot) 3? Sarasin, Geneva. 



Bonijol constructed a great number of electrical apparatus under the direc- 

 tion and with the advice of G. and A. de la Rive. 



