cies that is so adequate and practical as this annual gathering of scientific men in the different cities, and under the conditions secured by the American Association.
The problem of its success is one of social dynamics. There are resistances to be overcome in the shape of difficulties in bringing scientific men together from distant points, and of public apathy toward the interests of science. The American Association has been checked by these impediments, but it has made headway in spite of them. There has been a varying success at its different meetings, but on the-whole the most encouraging progress, which is signalized by the fact that the last meeting has been the most successful and satisfactory of all.
We print the able and interesting address of the retiring President, Dr. George F. Barker. It is a model discourse of its class, reporting the present state of knowledge upon a subject of grave interest, and in a style suited to all readers of general intelligence.
Dr. Lewis H. Morgan, of Rochester, presided with an easy dignity over the general sessions of the meeting, and he could not fail to be gratified with the increasing interest shown in the ethnological studies to which he has so long devoted himself, and of which he is now the most eminent American representative. The section dealing with these subjects had many instructive papers and a full attendance throughout the meeting.
Professor George J. Brush, of New Haven, was elected the next President, and will preside over the meeting to be held at Cincinnati, beginning August 17, 1881.
THE NEW PHOTOPHONE.
The most striking result brought out at the late meeting of the American Association had reference to the relations of sound and light, and was due to the joint labors of Mr. A. Graham Bell and Mr. Sumner Tainter, of Boston. The luminous ray, whether of sunlight or from an artificial source, was shown to be capable of transmitting articulate sounds, as the wire transmits them in the case of the telephone. The mechanical combination by which this effect is produced is called the photophone. We print in full Mr. Bell's paper describing the principle and mechanism of the contrivance, and the experiments by which it was elucidated and brought into shape. The metal selenium, discovered in the early part of the century, but hitherto of no practical use, here comes into prominence. It was known to have curious properties, shifting into allotropic forms with the most contrasted characters, and changing its electrical relations in a remarkable manner under the influence of light. Under the arrangements of the inventors, rays of light give rise to sound by impinging upon a surface of selenium—sounds which are audible through the telephone either as continuous musical notes of different pitches, or as vocal communications. Though it is said that light produces the effect, yet this is not strictly true; for a thick plate of India-rubber, if interposed in the path of the acting beam, intercepts all the light but still permits the passage of the radiant force which produces the sound. It is some dark ray accompanying the light proper that does the work. The experimenters have found also that other substances share with selenium the property here made available, though in a less degree. We thus have another step in the rapid progress of molecular physics and the marvelous interaction of forces which is sure to stimulate experimental inquiry, though whether it will confound past conclusions and clear up past mysteries it is impossible to say. And equally impossible is it to say whether the photophone will turn out to be of any practical use. But it is certainly
