Intelligence and Miscellaneous Articles. 323 



and as some flint implements, the genuineness of which is not 

 doubted, have been found in these deposits, the question of the 

 antiquity of man will not be affected, whatever the conclusions 

 arrived at with regard to certain others. 



XL VI. Intelligence and Miscellaneous Articles. 



BYT. STERRY HUNT, M.A., F.R.S. 



THE late researches of Tyndall on the relation of gases and 

 vapours to radiant heat are important in their bearing upon the 

 temperature of the earth's surface in former geological periods. 

 He has shown that heat, from whatever source, passes through 

 hydrogen, oxygen, and nitrogen gases, or through dry air, with 

 nearly the same facility as through a vacuum. These gases are thus 

 to radiant heat what rock-salt is among solids. Glass and some 

 other solid substances, which are readily permeable to light and 

 to solar heat, offer, as is well known, great obstacles to the passage 

 of radiant heat from non- luminous bodies ; and Tyndall has recently 

 shown that many colourless vapours and gases have a similar effect, 

 intercepting the heat from such sources, by which they become 

 warmed, and in their turn radiate heat. Thus while for a vacuum 

 the absorption of heat from a body at 212° F. is represented by 0, 

 and that for dry air is 1, the absorption by an atmosphere of car- 

 bonic acid gas equals 90, by marsh-gas 403, by olefiant gas 970, 

 and by ammonia 1195. The diffusion of olefiant gas of one inch 

 tension in a vacuum produces an absorption of 90, and the same 

 amount of carbonic acid gas an absorption of 5*6. The small quanti- 

 ties of ozone present in electrolytic oxygen were found to raise 

 its absorptive power from 1 to 85, and even to 136 ; and the watery 

 vapour present in the air at ordinary temperatures in like manner 

 produces an absorption of heat represented by 70 or 80. Air satu- 

 rated with moisture at the ordinary temperature absorbs more than 

 five hundredths of the heat radiated from a metallic vessel filled with 

 boiling water ; and Tyndall calculates that of the heat radiated from 

 the earth's surface warmed by the sun's rays, one-tenth is inter- 

 cepted by the aqueous vapour within ten feet of the surface. Hence 

 the powerful influence of moist air upon the climate of the globe. 

 Like a covering of glass, it allows the sun's rays to reach the earth, 

 but prevents to a great extent the loss by radiation of the heat thus 

 communicated. 



When, however, the supply of heat from the sun is interrupted 

 during long nights, the radiation which goes on into space causes 

 the precipitation of a great part of the watery vapour from the air, 

 and the earth, thus deprived of this protecting shield, becomes more 

 and more rapidly cooled. If now we could suppose the atmosphere 

 to be mingled with some permanent gas which should possess an 

 absorptive power like that of the vapour of water, this cooling pro- 



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