I. ELECTRICAL MACHINES, ETC. 299 



1234c. Electrical Machine, by Singer, used by Mr. Francis 

 Ronalds in his early experiments in the discovery of the electric 

 telegraph ; described in his work on the electric telegraph, 

 dated 1823. Kew Committee of the Royal Society. 



It is an ordinary cylinder machine of blue glass, standing on glass columns. 







1235. Bertsch's Machine. Frederick Guthrie. 



A negatively excited sheet of ebonite leans against a revolving disc of the 

 same material. On the other side of the revolving disc, one above and one 

 below, are electric rakes. The conductor in connexion with the lower rake 

 becomes negatively charged, the other one positively. 



1236. Holtz's Machine. Frederick Guthrie. 



A good example of this machine in one of its original forms, with windows 

 and armatures. It gives a current of sparks over an interval of 8 inches. 



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

 ebonite discs. Dr. L. Blcekrode, 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 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 

 ebonite 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 Poggendorff s Annalen, 

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



1241. Di-Electrical Machine. M. Carre. 



4560. Photograph of the " Cecchi Electrical Machine," 



formed of two discs, which are placed partially one over the other, 

 the one of caoutchouc, and the other of glass, with parallel axes. 



Prof. Filippo Cecchi, Florence. 



