A NEW TELEPHONE.

Nelson Evening Mail, Volume XVI, Issue 123, 25 May 1881, Page 4

A NEW TELEPHONE.

A paper "On the Conversion of Radiant Energy into .Sonorous Vibr - tions" was read before the Royal Society by Mr "W. H. Preece, the electrician to the Post Office. The remarkable discovery of Messrs Graham Bell and Summer Tainter'that the rapid intermittent incidence of rays of light on discs of hard substances produces sonorous vibrations has attracted very much attention and has excited much physical work to solve an unexpected problem. The advocates of the emission theory of light have striven for 200 years to obtain such a proof of their theory and have failed, "Why have Bell and Tainter succeeded, or have they succeeded at all ? May not their phenomena be due to some other cause than to the incidence of light ? It was suspected by many that it was a heat effect, and not a light one at all. M, Mercadier, in [Paris, have placed this beyond doubt, and now Mr Preece has completed the chain of evidence by a careful and elaborate inquiry into the cause of the phenomena. In the first part of his paper he has shown that ebonite and indiarubber, though opaque to the light rays, are remarkably diathermanous, or transparent to the heat rays, and therefore that radiant heat can act through screens of those materials. Indeed, ebouite is shown to be almost perfectly trarsparent to radiant heat, whilst it is absolutely impervious to light. He next shows by experiments made on veiy delicate apparatus that no more vibrations than six per second can possibly be produced by the direct impfect of -heat -waves causing expansion of the mass of the disc, and therefore that the Bell-Tainter effect is not due to the absorption of heat changing the volume of the hard substance experimented upon. He next inquires whether the effect observed is cue to a molecular pressure similar to that w bich produces the rotation. of the radiometer, for this being a mere surface action, the element of time is eliminated. Many experiments arer described which * were made with discs of. various kinds in different ways, but the. results were, bo unsatisfactory and variable that the question was. raised whether the discs vibrai ed at all. By the aid of microphones and specially constructed chambers, it is proved clearly that the undulations are those of the contained air, and not of the discs. In fact, the sounds were intensified by removing the discs. Moreover, the effects were materially assisted by coating the sides of the containing vessel wiih a substance highly absorbent of heat, such as the carbcn deposited by burning camphor. It is next shown that the effects are dependent on the number of heat ray a that paBB through the discs, and not on those'that are incident on- them, and that the greater the absorbent, character; of the air or 'vapour contained in the case, the more intense the; sounds' emitted. AIL these results are repeated; and shown with ordinary flasks lamp-i blacked on their exterior and interior. Finally it is Bhown that there is a time; element introduced, and that the loudn ness of the note emitted depends not! only on the 'rapidity with wliich.the contained air absorbs > the .radiant energy, but also on the rapidity witjh which it gives up its heat to the sides of the. case and the exits, open to it. It varies also with the form of the closed space, and with the character of the contained vapour, and with the diathermancy only, of the discs. The effect being thus due to radiant heat and its' absorption by suitable surfaces, it was next shown that if a spiral of wire be completely "enclosed in a lampblacked case, sounds we?e emitted when currents of electricity were rapidly and intermittently transmitted through the wire; and, moreover, that; when, these currents were produced --. by a; proper microphone transmitter articulate speech was reproduced. . Hence these phenomena! are simply effects of radiant heat, and they are due to the changes of volume jn absorbent gages pd yapo«w pro

duced by the absorption of thermometric heat in a confined' spaced All the varied end novel experiments which Mr Graham Bell performed when be was recently in Europe with solids, liquid and gases, with tubes, flasks, and discs, are thus brought within one simple explanation, and are due to a remarkable influence of degraded heat rayß on absorbent vapours. The final result of this inquiry bas heen, not only to unravel an exceedingly interesting scientific problem, but to produce another form of telephone based on a new principle.