Page:Popular Science Monthly Volume 13.djvu/381

Rh this work with such conspicuous success as the distinguished man to whom it was so fortunately intrusted.

It may be added that, in a business point of view, the establishment has been managed with great skill and efficiency. The amount of money received from Smithson, in 1838, was $515,000, to which was added in 1865 a residuary legacy of Smithson amounting to $26,000; and, notwithstanding that a large portion of the fund has been absorbed in building, all the plans of Prof. Henry have been carried out, and the fund now available exceeds $700,000.

How scientific discoveries run in groups, one thing suggesting another so quickly as to make an epoch, is just now illustrated anew in the field of acoustics, and with the usual result of rival claims and disputed priority. Following the telephone and growing out of it comes another remarkable revelation, that minute sounds may be magnified to the ear as minute objects are magnified by lenses to the eye.

The telephone, in transmitting sound, greatly reduces or minifies it, and it therefore became a problem for experimenters to find out how sounds can be transmitted with the least loss of volume and intensity. Mr. Thomas A. Edison early attacked this problem with his usual assiduity and fertile inventiveness. Operating upon many hundred substances of diverse qualities and in varying conditions to test their sonorous capacities under electrical influence, he found that carbon possesses this singular property in a very remarkable degree. He found, moreover, that the effect varies with the pressure upon the carbon, and, what is more astonishing still, that it varies so greatly with the small differences of pressure produced by the passage of sound waves as to alter the flow of the electrical current. More than a year ago he embodied this principle in the "carbon telephone," by which the capacity of the instrument was greatly augmented.

But now Prof. D. E. Hughes, already well known as the inventor of the type-printing apparatus that bears his name, comes forward with an arrangement involving the same property of the same substance, but developing almost incredible effects. He claims to have reached these results in his own way, as follows: Following a hint of Sir William Thomson in regard to the molecular change and conductivity of wires under mechanical strain, he inserted a stretched and strained wire in his telephonic circuit. But no effect was produced until it broke, when a sound was given out so curious and marked that Prof. Hughes followed it up, by pressing the broken ends together, when the new effect was faintly reproduced. Following this suggestion, he introduced other pieces so as to have broken or imperfect connections, when the faint sounds were improved. Iron nails or a steel watch-chain also answered the purpose.

Prof. Hughes says he found the same property in porous charcoal, and that it was heightened by infiltrating the carbon with metallic mercury. The part introduced into the circuit Prof. Hughes calls the "transmitter," and the arrangement which he recently exhibited to the Royal Society consists of a glass tube two inches long, and one-fourth inch in diameter, filled with a series of plugs of mercurialized carbon, the end-plugs being attached to the wires of the circuit. He uses a small three-celled galvanic battery to furnish the current, and, with the transmitter introduced, sounds otherwise perfectly inaudible by the ear are not only heard, but are conveyed to great distances by the telephone. The surprising thing is that when these pieces of carbon barely touch each other the electric current