299 



SCIENTIFIC SIDE-LIGHTS 



Heat 



would have been shortened, whereas its 

 length has certainly not diminished during 

 that period by ^iUth of a second. LYELL 

 Principles of Geology, bk. i, ch. 8, p. 129. 

 (A., 1854.) 



' 1458. HEAT OF HUMAN BODY En- 

 ergy Expended in Maintaining Other Ex- 

 penditures of Energy. The amount of en- 

 ergy daily manifested by the adult human 

 body in (a) the maintenance of its tem- 

 perature ; (b) in internal mechanical work, 

 as in the movements of the respiratory mus- 

 cles, the heart, etc.; and (c) in external 

 mechanical work, as in locomotion and all 

 other voluntary movements, has been reck- 

 oned at about 3,400 foot-tons. Of this 

 amount only one-tenth is directly ex- 

 pended in internal and external mechanical 

 work, the remainder being employed in the 

 maintenance of the body's heat. The latter 

 amount represents the heat which would be 

 required to raise 48.4 Ibs. of water from the 

 freezing- to the boiling-point; or, if con- 

 verted into mechanical power, it would suf- 

 fice to raise the body of a man weighing 

 about 150 Ibs. through a vertical height of 

 8% miles. 



To the foregoing amounts of expenditure 

 must be added the quite unknown quantity 

 expended in the various manifestations of 

 nerve-force, and in the work of nutrition 

 and growth (using these terms in their 

 widest sense). By comparing the amount 

 of energy which should be produced in the 

 body, from so much food of a given kind, 

 with that which is actually manifested (as 

 shown by the various products of combus- 

 tion in the excretions ) , attempts have been 

 made, indeed, to estimate, by a process of 

 exclusion, these unknown quantities; but 

 all such calculations must be at present con- 

 sidered only very doubtfully approximate. 

 BAKER Handbook of Physiology, vol. ii, ch. 

 17, p. 65. (W. W., 1885.) 



1459. 



Loss of, in Exercise 



Exertion Creates New Supply. It would 

 appear . . . that the body ought to 

 grow colder, in the act of climbing or of 

 working [since heat is thrown off from the 

 body into space], whereas universal experi- 

 ence proves it to grow warmer. The solu- 

 tion of this seeming contradiction is found 

 in the fact that, when the muscles are ex- 

 erted, augmented respiration and increased 

 chemical action set in. The fan which urges 

 oxygen into the fire within is more briskly 

 moved; and thus, tho heat actually disap- 

 pears as we climb, the loss is more than 

 covered by the increased activity of the 

 chemical processes. TYNDAIX Heat a Mode 

 of Motion, lect. 17, p. 531. (A., 1900.) 



146O. Loss of, through 



Inanition Death by Starvation Is Death by 

 Cold External Warmth in Exhaustive Dis- 

 eases. It has been often said, and with 

 truth, altho the statement requires some 

 qualification, that death by starvation is 

 really death by cold; for not only has it 



been found that differences of time with re- 

 gard to the period of the fatal result are 

 attended by the same ultimate loss of heat 

 [about 30 P.], but the . . . applica- 

 tion of external warmth to animals cold and 

 dying from starvation is [found to be] more 

 effectual in reviving them than the adminis- 

 tration of food. In other words, an animal 

 exhausted by deprivation of nourishment is 

 unable so to digest food as to use it as fuel, 

 and therefore is depenctent for heat on its 

 supply from without. Similar facts are 

 often observed in the treatment of exhaust- 

 ive diseases in man. BAKER Handbook of 

 Physiology, vol. i, ch. 7, p. 220. (W. W., 

 1885.) 



1461. HEAT OF THE ATMOSPHERE 



Chill of Upper Air Absolute Zero of 

 Space. If we suddenly compress a cubic 

 foot of air at ordinary pressure into a cubic 

 inch of space, that cubic inch will be very 

 hot because it contains all the heat that was 

 distributed through the entire cubic foot be- 

 fore the compression took place. Now let it 

 remain compressed until the heat has radi- 

 ated from it, as it soon will, and the air be- 

 comes of the same temperature as the sur- 

 rounding air. What ought to happen if 

 then we should suddenly allow this cubic 

 inch of air to expand to its normal pressure, 

 when it will occupy a cubic foot of space? 

 Inasmuch as we allowed the heat to escape 

 from it when in the condensed form, when 

 it expands it will be very cold, because the 

 heat of the cubic inch, now reduced to the 

 normal temperature of the surrounding air, 

 is distributed over a cubic foot of space. 

 This is precisely what takes place when 

 heated air at the surface of the earth 

 (which is condensed to a certain extent) 

 rises to the higher regions of the atmos- 

 phere. There is a gradual expansion as it 

 ascends, and consequently a gradual cooling, 

 because a given amount of heat is being con- 

 stantly distributed over a greater amount of 

 space. At an altitude of forty-five miles it 

 will have expanded about 25,000 times, 

 which will bring the temperature down to 

 between 200 and 300 degrees below zero. 

 When we get beyond the limits of the atmos- 

 phere we get into the region of absolute 

 cold, because heat is atomic motion, and 

 there can be no atomic motion where there 

 are no atoms. ELISHA GRAY Nature's 

 Miracles, vol. i, ch. 7, p. 54. (F. H. & H., 

 1900.) 



1462. HEAT, PLANTS NEED UNI- 

 FORM Light May Vary More. There is every 

 reason to conclude that the range of inten- 

 sity of light to which living plants can ac- 

 commodate themselves is far wider than 

 that of heat. No palms or tree-ferns can 

 live in our temperate latitudes without pro- 

 tection from the cold; but when placed in 

 hothouses they grow luxuriantly, even un- 

 der a cloudy sky, and where much light is 

 intercepted by the glass and frame-work. 

 At St. Petersburg, in lat. 60 N., these 

 plants have been successfully cultivated in 



