1GO ANNUAL OF SCIENTIFIC DISCOVERY. 



Irishes a constant supply of electricity, and the action of the ma- 

 chine is remarkably powerful. 



Holtz's machine depends on similar principles; it is described 

 in " Poggendorff' s Annalen," cxxvii. 320. A simpler form is de- 

 scribedljy Bertscli in *' Cosmos," No. 7, 1866. All these instru- 

 ments are much more powerful than plate electrical machines of 

 the same size, and they have'the advantage of working with but 

 a small application offeree. American Journal of Science, March, 

 1867, from Pogg. Ann. cxxv. 469. 



NEW FORMS OP THE HOLTZ MACHINE. 



M. Bertsch, in the " Comptes Rendus," Vol. 63, p. 771, describes 

 a form of the Holtz machine, as modified by himself; though an- 

 alogous in form, the generator is very different. It is composed 

 of a single disc of isolating substance, instead of two, so that the 

 action of a layer of interposed air in the production of the phe- 

 nomena need not be considered. The disc, a thin sheet of isolat- 

 ing substance, is mounted on a shaft of the same, and can, by a 

 handle, be rotated 10 or 15 times in a second. Two collec- 

 tors with metallic points, not connected, are placed perpendicu- 

 larly to the plane of the disc, at opposite extremities of its diame- 

 ter, and serve as the origin of the manifestation of the double 

 current which is created. Each collector is furnished with a mov- 

 able arm, serving as an electrode, ending with a ball, and they 

 separate from each other at right angles, or approach until they 

 meet. A conductor with a large surface is connected with one of 

 these poles, to increase the tension. 



Behind the plate, and parallel to it, can be placed one or more 

 sectors or thin plates of isolating material, not in contact with 

 the last, but at a little distance from it ; these can act either alone, 

 or superposed one on another ; they are of about 60 degrees each, 

 of a triangular shape, and serve as inductors. 



To start the machine, one of the sectors is rubbed lightly with 

 the hand, which electrifies its surface, and placed in the position 

 indicated ; the wheel being put in motion, a series of sparks with- 

 out intermission spring between the two electrodes. The appa- 

 ratus remains charged, whether the motion of the wheel is inter- 

 rupted or not, as does the ordinary electrophorus. In a dry 

 atmosphere the flow of electricity will last for several hours with- 

 out any sensible diminution : this seems to prove theoretically that 

 it would continue indefinitely if the air was absolutely isolated. 

 If a second sector be added behind the first, equally electrified by 

 friction, the quantity of electricity is doubled, without increasing 

 the tension, because the surface of the conductor remains the 

 same ; a third and fourth sector superposed on the first, so many 

 new inductors, increase the quantity, which is limited only by the 

 distance of the electrified surfaces, the diameter, the rapidity of 

 the wheel, and the promptness with which it regains equilibrium 

 by the electrodes. With a disc of 50 centimetres of hardened 

 rubber and movement of 10 turns a second, and 2 sectors, can 

 be obtained almost uninterrupted sparks of 10 to 15 centimetres 



