J. ELECTRICAL MACHINES, ETC. 301 



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

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

 and negative electricity. 



The Council of King' s College, London. 



1244. Nairne's Early Electrical Machine, with glass 

 globe. The Council of King's College, London. 



1245. Cylinder Electrical Machine. 



The Council of King's College, London. 



1246. Plate Electrical Machine, with four rubbers. 



The Council of King's College, London. 



1247. Armstrong's Electric Boiler or Hydro-Electric 

 Machine. The Council of King's College, London. 



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

 by means of an electric spark. 



The Council of 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. 



1729. Glass Globes for producing Electricity by rubbing 

 with the hand. The Council of King's College, London. 



The globes are caused to revolve by means of multiplying wheels and a 

 band of rope. The globes may be exhausted, and they then become luminous ; 

 the greatest amount of electricity or " fire " was obtained from them when 

 they were exhausted. In the one with a large brass cap, a small wooden disc 

 could be inserted with threads distributed round its edge ; when the globe 

 was excited the threads stood out from the edge of the disc. Constructed 

 about A.D. 1720.- 



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



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

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

 keep electric charges for 14 days, or 14 times longer than the glass jars of 

 Kirchhoff. 



The advantages of this instrument are: (1.) That the quadrants with 

 the needle and mirror can be easily removed, so that any change in the needle 

 or misplacement of the mirror may be examined with certainty. 



There are new arrangements in the Leyden jar for raising or turning the 

 needle without shaking the entire instrument (a thing to be avoided). 



1249b. Combined Holtz's and Bertch's Induction Ma- 

 chine, with arrangement for separating the same. 



Harvey, Reynolds, and Co. 



