_Experiments by M. Hellesen, of Copenhagen._--In order to estimate the reciprocal effects of different parts of a telephone, M. Hellesen has made telephones of the same size with three different arrangements which act inversely to each other. The first was of the ordinary form, the second like that of Bell’s first system, that is, with a membrane supporting a small iron armature on its centre, instead of a vibrating disk, and the third telephone consisted of a hollow cylindrical magnet, with the vibrating disk fixed to one of its poles, and the disk was adapted to move before a flat, snail-shaped spiral, of which the number of spirals equalled those of the two other helices. In this last arrangement, the induced currents resulting from the vibrations of the voice might be assimilated to those which follow from the approximation and withdrawal of the two parallel spirals, one of which should be traversed by a current. It is this last arrangement which Mr. Bell has adopted as producing the best effects, and it is rare in the history of discoveries that an inventor hits at once on the best arrangement of his instrument. _Experiments by M. Zetsche._--There are always a few perverse minds, impelled by a spirit of contradiction to deny evidence, and thus they attempt to depreciate a discovery of which the glory irritates them. The telephone and the phonograph have been the objects of such unworthy criticism. It has been said that electric action had nothing to do with the effects produced in the telephone, and that it only acted under the influence of mechanical vibrations transmitted by the conducting wire, just as in a string telephone. It was in vain to demonstrate to these obstinate minds that no sound is produced when the circuit is broken, and in order to convince them M. Zetsche has made some experiments to show, from the mode in which sound is propagated, that it is absurd to ascribe the sound produced in a telephone to mechanical vibration. He wrote to this effect in an article inserted in the ‘Journal Télégraphique,’ Berne, January 25, 1878: ‘The correspondence by telephone between Leipzig and Dresden affords another proof that the sounds which reproduce words at the receiving station are due to electric currents, and not to mechanical vibrations. The velocity with which sound is transmitted by vibrations on the wire, in the case of longitudinal undulations, may be estimated at three miles one furlong a second, so that the sound ought to traverse the distance from Leipzig to Dresden in 25 seconds. The same time ought to elapse before receiving the answer. Consequently there should be an interval of more than three-quarters of a minute allowed for each exchange of communication, which is by no means the case.’