38 Mr. Alexander Siemens [Feb. 3, 



was shown here by Nikola Tesla in connection with bis lecture on 

 alternate currents of high frequency ; but I want to show you that 

 high tension and low frequency produce the same effect. 



The next experiment was suggested by Dr. Obach, and the appa- 

 ratus employed in it is shown in Diagram 5. A copper conductor 

 (thickly insulated with indiarubber) is placed in a brass tube, and the 

 annular space between them is filled with coloured water which com- 

 municates with a vertical glass tube inserted in the centre of the 

 horizontal brass tube. One conductor from the high-tension trans- 

 former is connected to the insulated copper conductor, and the other 

 to the brass tube. Under these conditions no current passes, but the 

 electric stress heats the insulating material, which shows itself by the 

 rise of the coloured liquid in the glass tube. 



Werner Siemens called attention to this phenomenon in a paper 

 contributed to Poggendorf 's Annalen in 1857, in which he commu- 

 nicated a series of experiments on electrostatic induction, proving, as 

 he expressly stated, the correctness of Faraday's theory of molecular 

 induction. 



Not very long ago Signor Riccnrdo Arno showed that a cylinder 

 of insulating material, brought under the influence of a rotary field 

 and suitably suspended, would commence to revolve, thus showing 

 that molecular movement was set up in it. He produced this effect 

 by means of an apparatus, a copy of which you see before you. A 

 hollow cylinder of gutta-percha is suspended on the point of a needle, 

 so that it can be made to turn with very little friction. Around it 

 are placed four vertical metal strips to which the high-tension current 

 is brought, as shown in Diagram 6. Between the two terminals of 

 the high-tension circuit, a connection is made by an inductionless 

 resistance in the shape of a U-tube filled with water and a condenser. 

 Two of the metal strips opposite each other are joined to the ends of 

 the inductionless resistance and the other two strips are connected to 

 the condsnser. In this way there is a difference of a quarter of a 

 phase between the two currents, and a rotating field is produced, 

 which causes the cylinder to revolve on account of the electrical 

 hysteresis set up. When the current is reversed the cylinder 

 revolves in the opposite direction. This result also obtains in the 

 case of a glass beaker which is inverted and supported by a pin- 

 point. 



Wood, slate, and marble are usually reckoned to be insulating 

 materials, but you will see that they do not offer a protracted resis- 

 tance to a current of high potential. When the electric spark passes 

 through marble it converts the carbonate of lime into quicklime, as 

 can readily be shown by moistening the broken surface with phenol- 

 phthalein, which leaves the carbonate of lime white and colours the 

 quicklime a beautiful pink colour. Even glass is pierced ; and we 

 must confess that at present we have no very reliable means of dealing 

 with electricity of very high pressure. 



