I. ELECTRICAL MACHINES, ETC. 259 



1237. Electrical Machine, based on Holtz's principle, with 

 ebonite discs. Dr. L. Bleekrode, The Hague, Holland. 



This machine is constructed for generating electricity on the principles of 

 induction as first employed by Holtz. The form is very much simplified, 

 and the only material used is ebonite (india-rubber combined with sulphur). 

 Two forms are constructed by the exhibitor ; the single ebonite machine 

 with one fixed disc and another rotating before it, and the double ebonite 

 machine. The latter consists of one fixed disc with paper armatures placed 

 in the ordinary way but on both sides, a double system of conductors, and 

 two rotating discs. The construction is no more complicated than that of the 

 single machine, yet the quantity of electricity is exactly doubled. 



[The single electrical machine is exhibited ; the double electrical machine 

 will, perhaps, be sent during the course of the Exhibition.] 



The advantages of the machines constructed in this way, supported by ex- 

 perience of more than two years, may thus be briefly stated : 



(1.) The ebonite machines, constructed on the system of the exhibitor, with 

 ebonites of a good quality (which may be easily had but must be care- 

 fully chosen) are at least as powerful in their action as the machines 

 with glass discs, but they surpass them in being less costly, not 

 liable to be broken, and much less dependent on the condition 

 of the atmosphere. This must be appreciated in England, where, as 

 is the case in Holland, glass electrical machines (working by 

 induction) often remain inoperative owing to atmospheric moisture. 

 (2.) Although of very simple construction, they are very useful and power- 

 ful machines. 



(3.) From a theoretical point of view they present many interesting pro- 

 perties when compared with machines in which glass is employed, 

 and this led to the conclusion that they differ in their mode of 

 producing electricity. An experimental investigation of this machine, 

 stating its peculiarities, has been published in PoggendorfFs Ajinalen, 

 1875, No. 10, pp. 278, 279. 



1238. The First Instrument used to Electrify the Ink 



Bottle of the Syphon llecorder. Sir W. Thomson. 



This was the first instrument used for producing the electricity required to 

 electrify the ink bottle of the syphon recorder. What is now known as the 

 mouse-mill, referred to in Clerk Maxwell's " Electricity and Magnetism," is a 

 modification of this instrument, driven by intermittent electro-magnetic force. 

 Described in Thomson's reprint of " Papers on Electro-statics and Magnet- 

 ism," xxiii. 416-419. 



1239. Modified form of 1238. Sir W. Thomson. 



1240. Further developed form of 1238. 



Sir W. Thomson. 



One of the applications of this is to multiply indefinitely the electro-static 

 indications obtainable from a feebly electrified body on the same principle as 

 Nicholson's Revolving Doubler, and as the rotating induction instrument 

 exhibited by Mr. C. F. Varley at the International Exhibition of 1861. 



1241. Di-Electrical Machine. M. Carre. 



1242. Holtz' Machine, with four plates. M. Ruhmhorff. 



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