260 SEC. 10. - ELECTRICITY. 



12 42 a, New form of Holtz' Machine. 



Francis Pizzorno, Bologna, Italy. 



1242b. Fixed Disc for a Holtz' Machine. 



Augustus Righi, Professor of Natural Philosophy (Phy- 

 sics) of Bologna (Italy). 



The greatest possible difference of potential between the conductors of a 

 Holt 2' machine depends on the difference of the potentials of the paper sur- 

 faces carried by the fixed disc. But this latter difference is limited by the 

 discharges which continually occur along the fixed disc. I have joined per- 

 pendicularly on the fixed disc an ebonite plate, which separates it into two 

 parts, so that the discharges must follow the two faces of the plate. The 

 potentials of the paper surfaces are increased, and the sparks between the con- 

 ductors become longer. 



This machine possesses four rows of points, namely, the two rows of points 

 of the conductors, and the two rows of points oblique communicating. 



1243. Old Electrical Machine, with glass cylinders, one of 

 which is covered with sealing wax> so as to obtain both positive 

 and negative electricity. 



Museum of King George III., King's College. 



1244. Nairne's Early Electrical Machine, with glass 



Museum of King George III., King's College. 



1245. Cylinder Electrical Machine. 



Museum of King George III., King's College. 



1246. Plate Electrical Machine, with four rubbers. 



Museum of King George III., King's College. 



1247. Armstrong's Electric Boiler or Hydro-Electric 

 Machine. Museum of King George III., King's College. 



1248. Volta's Electric Lamp, or apparatus for lighting gas 

 ~by means of an electric spark. 



Museum of King George HI., King's College, London. 



It contains a leaden bottle for the generation of hydrogen gas. In the 

 orifice are two wires separated from each other, which are connected to the 

 two plates of an electrophorus. One of the wires is connected with the tap, 

 so that the upper plate of the electrophorus is raised at the same time that 

 the hydrogen is allowed to escape at the orifice, and the spark from the 

 electrophorus sets fire to the hydrogen and thus lights the lamp. 



1249. Induction Electric Machine. T. Rob. Voss, Berlin. 



As there is no glass in Germany which insulates perfectly, Professor 

 Helmholtz has used Ley den jars made of ebonite or vulcanite, which can 

 keep electric charges for 14 days, and so 14 times longer than the glass jars 

 of Kirchhoff. 



