Page:Popular Science Monthly Volume 15.djvu/875

 of a metallic diaphragm. This arm or bar is a lever, and multiplies the scope of vibration. The current which is transmitting a message vibrates the diaphragm. In proportion to the strength of the wave of electricity on the wire, the friction between the arm and the cylinder is varied, and the amount of sound produced is varied in like proportion. The sound transmitted is thus magnified. The person who talks furnishes the power, but the person who is at the receiving instrument controls the power, and the message only becomes audible when the chalk cylinder is rotated. This receiving instrument has no connection with the wires that transmit the message, owing to defects not yet overcome in the manufacture of telegraph wires. It takes its message through a coil placed in close proximity to a second coil which is in communication with the ordinary telegraph wire. Could the coil be dispensed with, the sounds could be still more magnified than they are with the present arrangement. The instrument exhibited was only an experimental model; nevertheless it transmitted messages which were heard by the whole audience, numbering fifteen hundred persons.

Experiments on the Living Brain.—At the close of one of the daily sessions of the Association, Professor Burt G. Wilder gave illustrations of some of the experiments of Ferrier on the brains of living animals. Having by the use of ether reduced a cat to the state of insensibility, Professor Wilder laid bare the surface of the animal's brain by removing the roof of the skull. On the wall was hung a diagram of the brain, with certain regions of it designated by figures. A chart stated what movements would be made by the cat, as these different regions of its brain were successively touched by the terminals of a weak electric current, and in every case the movements occurred precisely as laid down in the chart. Thus, when the place on the brain answering to that marked "1" in the diagram was touched, the opposite hind-leg of the animal was advanced as the chart said it would be. When "4" was touched the opposite fore-leg moved as if to strike, being first drawn back. Again, the animal was made to scream, spit, and lash its tail, by similar means.

Insect-Destruction of Evergreen-Trees.—Professor S. H. Scudder gave to the members of the Entomological Club, an annex of the Association, an interesting account of the destruction of the pine-forests of Nantucket Island. Formerly, he said, the island was well wooded; but, during the war with England in 1812, the inhabitants, cut off from intercourse with the mainland, were reduced to such straits for fuel that they burned every tree. Some years ago plantations of pines were begun, and now a large portion of the island is covered with pines and scrub-oaks. Now, however, sure though slow destruction threatens the young forest through the agency of a small moth, whose larvae attack the leaf-buds. This moth is closely allied to the Retinea silvestrina of Europe, but probably belongs to a distinct species. It bores into the tip of each terminal bud, and saps the life of the tree. Every pine on the island, Mr. Scudder says, is affected, and he sees no way to save the forest. Other members reported the presence of Retinea and allied species of insects in different parts of the country. Professor J. H. Comstock had found a large species of Retinea destroying pine-trees in western New York. Mr. Bassett said that a few years ago the white pines and Norway spruces in Connecticut were threatened with destruction by a moth, but the danger passed away. Professor Riley said that the junipers on Long Island are attacked everywhere by a destructive moth, and that all the foreign imported evergreens suffered in like manner. He recommended the use of Paris-green as a means of exterminating the pests.

The Constitution of the Sun.—Professor S. P. Langley, Vice-President, addressed Section A upon the progress of solar physics. Even after the invention of the telescope, he said, astronomy was more concerned with the motions of the heavenly bodies than with their physical nature. With the aid of mathematics, the great law of gravitation was ascertained, and the movements of the heavenly bodies thenceforth could be predicted. But great questions still remained untouched. Life on the earth depends on the great central fire, the sun. What is that fire? What are its sources? How long will it continue? With almost the sole