Page:Popular Science Monthly Volume 45.djvu/589

Rh trees are fifteen feet in diameter and live to a great age. A group of trees in the province of Toosa, about a century old, are estimated to be equivalent to about forty thousand pounds of crude camphor. The camphor is extracted from chips taken from the roots or from the stem near the root, the wood yielding about five per cent of camphor, and the root a larger proportion. The annual export of Japan camphor averages about five million pounds. The forests in Japan owned by the people are now almost denuded of timber, but the Government still possesses large woods of camphor trees, which, it is estimated, will maintain a full average supply of the gum for the next twenty-five years. Plantations of young trees are also making and well taken care of; and although camphor has not hitherto been extracted from trees less than seventy or eighty years old, it is expected that under the present intelligent management equally good results may be realized in twenty-five or thirty years. The Japanese Department of Forests, which has the control of these woods, is under good management.

Constitution of the Ether.—Assuming that the elastic solid theory of the ether has failed, Mr. R. T. Glazebrook thinks that the properties of the ether which would lead to the equations that represent the laws of the transmission of light, may be found in the labile ether of Lord Kelvin. This is an elastic solid, or quasi solid incapable of transmitting normal waves. Such a medium would collapse unless of infinite extent, or else fixed at its boundaries. A soap bubble affords in two dimensions an illustration of it, the tension being independent of its dimensions. Waves of displacement parallel to the surface of the film would not be transmitted. But such a film in consequence of its tension has an apparent rigidity for displacements normal to its surface; it can transmit transverse waves with a velocity which depends on the tension. Now the labile ether is a medium which has, in three dimensions, characteristics resembling those of the two dimensional film. Given such a medium—and there is nothing impossible in its conception—and the main phenomena of light follow as a necessary consequence. Lord Kelvin, again, has shown us how such a medium might be made up of molecules, having rotation in such a way that it could not be distinguished from an ordinary fluid in respect to any rotational motion; it would, however, resist rotational movements with a force proportional to the twist, just the force required. The medium has no real rigidity, but only a quasi rigidity conferred on it by its rotational motion. The actual periodic displacements of such a medium may constitute light. We may claim, then, with some confidence, to have a mechanical theory of light. But nowadays the ether has other functions to perform, and there is another theory to consider, which at present holds the field. Maxwell's equations of the electro-magnetic field are practically identical with those of the quasi-labile ether. The symbols which oocuroccur [sic] can have an electromagnetic meaning; we speak of permeability and inductive capacity instead of rigidity and density, and take as our variables the electric or magnetic displacements instead of the actual displacement of the rotation. Still, such a thing is not mechanical, and we have no satisfactory mechanical theory of the electro-magnetic field. But the theory of the quasi-labile ether may be applied, and gives two analogies according as we regard the density of the medium to be analogous to electrostatic inductive capacity or to magnetic permeability.

Explorations in Thibet.—In a paper on Recent Explorations in Thibet, Mr. E. Delmar Morgan said in the British Association that the discoveries made by travelers, beginning with the Schlagintweit brothers and ending with Dr. Thorold's recent journey, had opened out new fields of research in hitherto inaccessible parts. They had determined the continuity of the Kuen Luen mountain system through twenty degrees of longitude, and made known the direction and structure of the principal chains. They had shown the lacustrine character of the central plateaus, and traced almost to their sources some of the mightiest rivers of Asia. They had thrown light on the climatic conditions of these lofty deserts, and seen an abundance of animal life on them. Their researches had proved the existence, in former times, of a line of flourishing oases along the northern foot of the Kuen Luen,