_M. Hellesen’s Reaction Telephone._--M. Hellesen believed that the vibrations produced by the voice on the carbon of a telephonic sender would be magnified if the moveable part of the rheotome were subjected to an electro-magnetic action resulting from the vibrations themselves, and he has contrived a sender, which is based on the principle shown in fig. 33, and which has the merit of forming in itself the inducing apparatus intended to transform the voltaic currents employed. This instrument is composed of a vertical iron tube, supported on a magnetic bar N S, and surrounded by a magnetising coil B B, above which is fixed an inducing helix of fine wire I I, communicating with the circuit. Within the tube there is a lead pencil C, held by a porte-crayon which can be raised or lowered by means of a screw V fixed below the magnetic bar. Finally, above this pencil, there is an iron vibrating plate L L, with a platinum point in communication with the battery in its centre; the local circuit communicates with the pencil by means of the magnetising helix B, and for this purpose one end is soldered to the iron tube. From this arrangement it follows that the vibrations of the plate L L, at the moment when it comes nearest to the pencil, tend to become greater in consequence of the attractive force exerted on the plate, and as the pressure of the lead pencil is increased, it increases the differences of resistance which result from it, and consequently causes greater variations in the intensity of the transmitted currents. _Reaction Telephone of Messrs. Thomson and Houston._--The telephonic arrangement we have described has lately been adopted by Mr. Elihu Thomson and Mr. Edwin J. Houston, who, on June 21, 1878, two months after M. Hellesen explained his system to me,[7] published an article in ‘The English Mechanic and World of Science’ about an instrument very similar to that of M. Hellesen.