571 



SCIENTIFIC SIDE-LIGHTS 



Qualifications 



firmament, was a very natural one. They 

 seemed to revolve around the earth every 

 day for generation after generation without 

 the slightest change in their relative posi- 

 tions. If there were no solid connection be- 

 tween them, it does not seem possible that a 

 thousand bodies could move around their 

 vast circuit for such long periods of time 

 without a single one of them varying its 

 distance from one of the others. It is espe- 

 cially difficult to conceive how they could all 

 move around the same axis. But when they 

 are all set in a solid sphere, every one is 

 made secure in its place. The planets could 

 not be set in the same sphere, because they 

 change their positions among the stars. 

 This idea of the sphericity of the heavens 

 held on to the minds of men with remark- 

 able tenacity. The fundamental proposition 

 of the system, both of Ptolemy and Coper- 

 nicus, was that the universe is spherical, the 

 latter seeking to prove the naturalness of 

 the spherical form by the analogy of a drop 

 of water, altho the theory served him no 

 purpose whatever. Faint traces of the idea 

 are seen here and there in Kepler, with 

 whom it vanished from the mind of the race, 

 as the image of Santa Glaus disappears 

 from the mind of the growing child. NEW- 

 COMB Popular Astronomy, pt. i, int., p. 4. 

 (A. B. Co.) 



2818. RADIATION FROM LEAVES 



Space Draining Plants of Heat Death of 

 Leaves that Cannot Turn. We doubted at 

 first whether radiation would affect in any 

 important manner objects so thin as are 

 many cotyledons and leaves, and more espe- 

 cially affect differently their upper and 

 lower surfaces; for altho the temperature 

 of their upper surfaces would undoubtedly 

 fall when freely exposed to a clear sky, yet 

 we thought that they would so quickly ac- 

 quire by conduction the temperature of the 

 surrounding air, that it could hardly make 

 any sensible difference to them whether 

 they stood horizontally and radiated into 

 the open sky, or vertically and radiated 

 chiefly in a lateral direction towards neigh- 

 boring plants and other objects. We en- 

 deavored, therefore, to ascertain something 

 on this head by preventing the leaves of sev- 

 eral plants from going to sleep, and by ex- 

 posing to a clear sky when the temperature 

 Avas beneath the freezing-point, these, as 

 well as the other leaves on the same plants 

 which had already assumed their nocturnal 

 vertical position. Our experiments show 

 that leaves thus compelled to remain hori- 

 zontal at night suffered much more injury 

 from frost than those which were allowed to 

 assume their normal vertical position. 

 DARWIN Power of Movement in Plants, ch. 

 6, p. 285. (A., 1900.) 



2819. RADIATION FROM METAL 



AND WOOL Protecting Cover Should Fit 

 Loosely. Here are two metal vessels, one 

 of which is covered with lampblack, while 



the other is bright. Three-quarters of an 

 hour ago boiling water was poured into 

 them, a thermometer being placed in each. 

 Both thermometers then showed the same 

 temperature, but now one of them is some 

 degrees below the other, the vessel which 

 has cooled most rapidly being the coated 

 one. Here, again, are two vessels, one of 

 which is bright, and the other closely coated 

 with flannel. Half an hour ago two ther- 

 mometers, plunged in these vessels, showed 

 the same temperature, but the covered vessel 

 has now a temperature two or three degrees 

 lower than the naked one. It is not unusual 

 to preserve the heat of teapots by a woolen 

 covering ; but to be effective the " cozy " 

 must fit very loosely. A closely fitting 

 cover which has the heat of the teapot freely 

 imparted to it by contact would, as we have 

 seen, promote the loss which it is intended 

 to diminish, and thus do more harm than 

 good. TYNDALL Heat a Mode of Motion, 

 lect. 11, p. 299. (A., 1900.) 



2820. RADIATION KEEPING PACE 

 WITH CONTRACTION Would Sustain 

 Sun's Heat for Millions of Years. Calcula- 

 tion shows that, assuming the thermal ca- 

 pacity of the sun to be the same as that of 

 water, the temperature might be raised to 

 28,000,000 of degrees, if this quantity of 

 heat could ever have been present in the sun 

 at one time. This cannot be assumed, for 

 such an increase of temperature would offer 

 the greatest hindrance to condensation. It 

 is probable rather that a great part of this 

 heat, which was produced by condensation, 

 began to radiate into space before this con- 

 densation was complete. But the heat 

 which the sun could have previously de- 

 veloped by its condensation would have been 

 sufficient to cover its present expenditure 

 for not less than 22,000,000 of years of the 

 past. HELMHOLTZ Popular Lectures, lect. 

 4, p. 181. (L. G. & Co., 1898.) 



2821. RAIN, SILENT ACTION OF 



Solid Rocks Dissolved " The Waters Wear 

 the Stones " (Job xiv, 19). The most con- 

 spicuous agent employed [in the disinte- 

 gration of rocks] is rain. Rain is not 

 chemically pure, but always contains some 

 proportion of oxygen and carbonic acid 

 absorbed from the atmosphere; and after it 

 reaches the ground organic acids are derived 

 by it from the decaying vegetable and ani- 

 mal matter with which soils are more or 

 less impregnated. Armed with such chem- 

 ical agents, it attacks the various minerals 

 of which rocks are composed, and thus, 

 sooner or later, these minerals break up. 

 . . . In all regions where rain falls the 

 result of this chemical action is conspicu- 

 ous; soluble rocks are everywhere dissolv- 

 ing, while partially soluble rocks are becom- 

 ing rotten and disintegrated. In limestone 

 areas it can be shown that sometimes hun- 

 dreds of feet of rock have thus been gradu- 

 ally and silently removed from the surface 

 of the land. And the great depth now and 



