M. Matteucci on the Voltaic Arc, 289 



soon decreased, was developed ; but it was of such extent 

 that the needle seldom came to perfect rest. By bracing the 

 muscles of the hand and arm only doubtful effects were ob- 

 tained, precisely as was found by the French experimenters. 

 As the needle oscillated somewhat rapid!}', seven to eight 

 seconds to one oscillation, I endeavoured to render its astatic 

 system more perfect, and succeeded in reducing the time of 

 vibration to thirty seconds, /. e. in increasing the sensitiveness 

 of the needle nearly sixteen times. 



Nevertheless the influence of the muscular contraction was 

 scarcely rendered more perceptible. Sometimes it was more, 

 sometimes less obscured by accidental deflections of the 

 needle, which it becomes the less possible to control the more 

 the magnetic directive force has decreased. Very little was 

 therefore to be expected from continuing to perfect the astatic 

 system, at least with the multiplier in use, the wire of which 

 did not appear to be entirely free from iron. Du Bois Rey- 

 mond obtained a higher degree of sensitiveness by means of a 

 larger number of convolutions, which is evidently preferable 

 in experiments of this nature. 



One method of observing the phaenomenon discovered by 

 Du Bois Reymond with less sensitive instruments, is by in- 

 creasing the electromotive action excited by muscular exer- 

 tion. Sixteen persons who took part in this experiment held 

 each other's moistened hands, and on all contracting simultane- 

 ously the right, or simultaneously the left arm, they formed, as 

 it were, a circuit of increased electromotive power. The effect 

 on the needle was now perfectly evident, and opposite accord- 

 ing as the right or left arm was contracted ; the direction of 

 the current was always from the hand to the shoulder. It is 

 essential that the muscular contraction should be increased, 

 or at least continued, until the needle begins to return, and 

 then suddenly discontinued. Although it was found impos- 

 sible to produce a greater deflection than 10° to 12°, the cor- 

 responding intensity of the current was sufficient to overcome 

 any accidental influences; nay, even to stop a movement in 

 the opposite direction and to reverse it. 

 Giessen, July 13, 1849. 



XXXVII. Observations on the Voltaic Arc. 

 By M. Matteucci *. 



I HAVE studied the calorific and luminous phaenomena of 

 the voltaic arc, and the transference of matter, with the 

 aid of the electro-magnetic machine which is now generally 

 * From the Comptes Rendus for September 3, 1849. 



Phil, Mag, S. 3. Vol. 35. No. 236. Oct. 1849. U 



