276 Prof. E. Wartmann's Sixth Memoir on Induction. 



held by its centre between two isolating clamps. Its funda- 

 mental tone was then ascertained, and the tones which cor- 

 respond to different modes of nodal subdivisions. The same 

 experiments were then repeated, after electrifying the lower 

 surface, the other being put in communication with the ground. 

 The fluid distributed over the latter exercised no influence on 

 the musical qualities of the plate. The only effect which in- 

 dicated its presence was a repulsion of the particles of sand 

 at the fixed point toward the common intersection of the dia- 

 meters. 



168. An iron wire, one metre long, was stretched on a mo- 

 nochord. It occupied the axis of a glass tube, on which was 

 rolled a thick copper wire covered with silk, and forming part 

 of the circuit of a Grove's battery of five pairs (139.). The 

 transversal and longitudinal sounds of the wire remained the 

 same as before the action of the current. 



169. A brass wire, arranged on the sonometer parallel to 

 the first, was tuned exactly in unison with it. An electro-magnet 

 excited by the five pairs was placed near the iron wire. Every 

 time the instrument was arranged so that the attraction of its 

 poles could not make the wire bend, the latter comported itself 

 like the brass wire. This was proved by the absence of beats 

 when they were made to sound together. 



170. In the preceding experiment the induction was distri- 

 buted over a great length. It might thence be feared that its 

 effect would be diminished on the nodal or ventral portions 

 of the wire. I therefore repeated these experiments with wires 

 of only m, 20 of copper and iron. In order to prevent any 

 temporary or permanent disfigurement resulting from the 

 different tensions to which they were subjected, I employed in 

 stretching them a mechanical artifice used in the suspension 

 of the threads of rheometers. It consists of a moveable nut 

 acting upon a screw terminated by a square prism, which slips 

 into a fixed hollow piece of the same section. The metallic 

 cord was attached at one end to an immoveable pin, and the 

 other to the extremity of the prism opposite to the screw. It 

 coincided with the axis of a bobbin m - 1 in length, and m, 032 

 external diameter, and which is perforated by an aperture 

 of m '01 1, in which were placed eleven concentric tin cylinders, 

 cut according to a generatrice and isolated from one another. 

 Each wire was made to vibrate transversely by means of the 

 bow, first in the natural state and then under the intense in- 

 duction of Grove's battery, without ever finding a difference 

 in the musical sound. The experiment was repeated with 

 different degrees of tension of the wires, and making them give 

 a numerous series of harmonics. The result never varied. 



