POPULAR MISCELLANY. 



569 



tributing ozone to the atmosphere ; and, as 

 the plants blossom in succession through 

 the season, this source of supply is in con- 

 stant 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 oxi- 

 dizing the organic matter that is always 

 present there. But, as flowering plants gen- 

 erate ozone in-doors during clear weather, it 

 can not be doubted that a living-room well 

 stocked with such plants would give off suf- 

 ficient 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 Pro- 

 fessor Riley's pamphlet on the subject, there 

 arc 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 larvae, 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 fe- 

 male moths are wingless, and can only reach 

 the tree-top by climbing up upon the bark. 

 They consist, therefore, principally in sur- 

 rounding the trunk of the tree with some- 

 thing 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 accom- 

 plish 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 dust- 

 ings to the trees. The worms have para- 



sitic 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 exter- 

 minated by the English sparrow. 



The Condition of the Earth's Interior. 



— Dr. M. E. Wadsworth has published a re- 

 view of the various hypotheses concerning 

 the condition of the earth's interior. Physi- 

 cists, reasoning from mathematical data, 

 suppose it to be solid ; but geological phe- 

 nomena 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 dif- 

 ficulties alleged by the physicists against 

 the theory of hquidity are of their own 

 making. They have taken premises that 

 no geologist would take, and have claimed 

 to apply points proved regarding these as- 

 sumed premises as proved for the whole 

 earth. It is not believed to be as yet pos- 

 sible mathematically to prove anything re- 

 garding the state of the earth's interior. 

 It is as necessary that physical and mathe- 

 matical discussions of the subject " should 

 conform to geological facts as it is that 

 geological theories should conform to phys- 

 ical and mathematical laws. It is incum- 

 bent on the physicist to explain earthquake- 

 motion, the rising and sinking of different 

 portions of the earth's crust, volcanic phe- 

 nomena, 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 de- 

 pends, in discussing the question of liquid- 

 ity, 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 solidifica- 

 tion 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 oth- 

 ers 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 



