Intelligence and Miscellaneous Articles. 223 



pole of the magnet of a Weber's magnetometer was submitted to 

 the simultaneous action of the south pole (surrounded by the coil) 

 of a telephone A and the south pole of a magnet ; these two 

 instruments were placed so that the bar of the magnetometer was 

 in equilibrium between them. A second telephone, B, was in 

 communication with A. The movements of the mirror of the 

 magnetometer were observed by the ordinary method of reflection 

 of the divisions of a rule in the field of a telescope. 



A pressure exerted upon the plate of B permitted a slight dis- 

 placement of the magnet to be ascertained • but the movement was 

 too small to be measured; its direction was always that which the 

 theory caused to be foreseen. 



Vibrations of the Plate. — Some attempts were made to determine 

 the vibrations of the plate. The first method employed consisted 

 in transmitting the vibrations to a gas-flame. For this purpose 

 the wide-mouthed bell of the telephone was replaced by a cylindrical 

 one of small capacity. A cork, pierced with two holes through 

 which passed two kneed tubes of glass, bounded within the cylinder 

 a sort of little chamber comprised between the front face of the 

 vibrating plate and the hind face of the cork. The illuminating- 

 gas entered through the first tube, and issued, forming a small 

 flame, at the extremity of the tapering second tube ; so that the 

 whole constituted something analogous to the manometric capsules 

 which M. Konig places upon the pipes. 



Every vibration of the plate is betrayed by a movement of the 

 flame when the induced currents employed are those produced by 

 a small Dubois-Eeymond coil, even when the exterior coil is at 2 

 centims. from the extremity of the inducing coil. The currents 

 produced by the voice in a second telephone cause no variation in 

 the height of the flame. 



The result was equally negative when a small mirror was borne 

 on a kneed lever with its end resting on the vibrating plate. A 

 ray of light reflected by the mirror did not appear to be displaced 

 under the influence of the vibrations produced by the voice. 



Finally, I tried to produce coloured rings between the vibrating 

 plate and a lens placed upon it. For this a very thin piece of glass 

 (Deekglaschen) was placed upon the vibrating plate, in contact 

 with the slightly convex lower face of a lens. The sounds were 

 transmitted by the instrument, although weakened. The coloured 

 rings were observed through a telescope furnished with a reticule. 



The displacement of a bright ring to the following dark one is 

 produced by a difference in the thickness of the stratum of air 

 equal to a quarter of a wave-length ; that is to say, a change in the 

 position of a yellow ring will be ascertained for about 0*000143 

 millim. displacement of the plate. This displacement is mani- 

 fested by a diminution in the distinctness of the rings, which 

 oscillate about their normal position. The displacements are 

 observed very distinctly by employing the induced currents of a 

 Dubois. Eeymond coil ; but it has not been possible to verify them 

 for the currents produced by the voice. 



Having heard it said that two telephones the localities of which 



