Page:Popular Science Monthly Volume 26.djvu/585

Rh ozone to the atmosphere; and, as the plants blossom in succession through the season, this source of supply is in constant operation. An interesting phase of the subject is the application of the results of the observations to the question whether plants should be cultivated in living-rooms. As a rule, ozone is not detectable in rooms, because it is constantly decomposed in oxidizing the organic matter that is always present there. But, as flowering plants generate ozone in-doors during clear weather, it can not be doubted that a living-room well stocked with such plants would give off sufficient to be of hygienic value. Important advantages may also be derived from the presence of foliage plants, even though they are incapable of producing ozone, for, if properly taken care of, they will contribute essentially to the maintenance of a hygienic degree of humidity in the atmosphere of the apartment.

The Canker-Worm—According to Professor Riley's pamphlet on the subject, there are two worms called the canker-worm, both destructive to apple, elm, and maple trees, and much alike. One is called the spring canker-worm, because the moths come out of the ground in the spring; the other, the fall canker-worm. The moths crawl up the tree and deposit their eggs upon the buds, where the larvæ, on being hatched out, begin at once to feed upon the tender leaves. The preventives against their appearance depend largely upon the fact that the female moths are wingless, and can only reach the tree-top by climbing up upon the bark. They consist, therefore, principally in surrounding the trunk of the tree with something in the nature of an obstacle that the worm can not climb by. The trunk may be tarred or greased, or a tin band may be tightly fastened around it. Such appliances are classified by Professor Riley into those which prevent the ascension of the moth by entangling her feet and trapping her fast, or by drowning her; and those which accomplish the same end by preventing her getting a foothold. Other remedies are to jar the trees and burn the worms in straw which has been laid at the bottom to catch them, and applying poisonous washings and dustings to the trees. The worms have parasitic foes, and hosts of industrious enemies among the birds, of which Professor Riley names more than forty species. In New York and Brooklyn they have been exterminated by the English sparrow.

'The Condition of the Earth's Interior,—Dr. M. E. Wadsworth has published a review of the various hypotheses concerning the condition of the earth's interior. Physicists, reasoning from mathematical data, suppose it to be solid; but geological phenomena can not be accounted for on that supposition, and various compromises have been proposed to meet the requirements of the case, which are not necessary if it can be shown that the theory of solidity is not well founded. It is suggested that the difficulties alleged by the physicists against the theory of liquidity are of their own making. They have taken premises that no geologist would take, and have claimed to apply points proved regarding these assumed premises as proved for the whole earth. It is not believed to be as yet possible mathematically to prove anything regarding the state of the earth's interior. It is as necessary that physical and mathematical discussions of the subject "should conform to geological facts as it is that geological theories should conform to physical and mathematical laws. It is incumbent on the physicist to explain earthquake motion, the rising and sinking of different portions of the earth's crust, volcanic phenomena, the uniformity in the composition of lavas, the structure of volcanic rocks, sedimentation, faulting, vein-formation, etc., by his theory of a solid crust." Much depends, in discussing the question of liquidity, upon the possibility of a solid body floating upon a liquid mass of the same substance, concerning which some writers hold that it must sink on account of its greater density, and thus compel solidification from the center. Experiments to test this point have given varying results, but show the possible existence of conditions under which the solid mass would float. Some elements solid are lighter than others liquid. The lighter solid crust would then rest on the denser liquid interior. The transition, moreover, from the solid to the liquid rock, is not sudden, as in the case of