826 Prof. Frankland on the Physical Cause 



This will be apparent from a consideration of the functions of 

 the three essential parts of the great natural glacial apparatus, 

 viz. the evaporator, the condenser, and the receiver. The part 

 performed by the ocean as the evaporator is too obvious to need 

 description. The two remaining portions of the apparatus, how- 

 ever, are generally confounded with each other. The mountains 

 are in reality the receivers or ice-bearers, and are only in a sub- 

 ordinate sense condensers. The true condenser is the dry air 

 of the upper region of the atmosphere, which permits of the free 

 radiation into space of the heat from aqueous vapour*, the latter, 

 as proved by TyndalPs recent researches, possessing extraordi- 

 nary powers of radiation and absorption. He has shown that 

 the watery vapour at the upper surface of a stratum of air satu- 

 rated, or nearly so, with moisture, must rapidly radiate its heat 

 into space and condense to rain or snow, according to the tem- 

 perature of the surrounding atmosphere, dry air being almost 

 completely powerless to arrest this radiation. Thus it is that 

 the enormous amount of heat developed by the condensation of 

 aqueous vapour is got rid of without any appreciable elevation 

 of the temperature of the medium in which the operation occurs. 

 That this process of condensation must be most active and im- 

 portant in meteorological phenomena can scarcely be doubted, 

 when it is considered that the great accession of heat to the sur- 

 rounding atmosphere, which occurs when aqueous condensation 

 takes place from any other cause, must soon put a stop to the 

 further deposition of moisture under such circumstances. Thus 

 the condensation of one cubic foot of water at 40° from aqueous 

 vapour at 32° F. would raise the temperature of 352,053 cubic 

 feet of air through 10°. Such an enormous accession of heat, 

 where condensation takes place without radiation, could not fail 

 promptly to arrest the process. 



Thus the condenser is an apparatus perfectly distinct from the 



* I have devised a simple mode of experimentally demonstrating the 

 radiation from aqueous vapour, so that the effect can be seen by a large 

 number of persons at once. A charcoal chauffer, 14 inches high and 6 

 inches in diameter, is placed about two feet from, and in front of, a thermo- 

 electric pile, the radiation from the chauffer and fuel being carefully cut off 

 from the pile by a double metallic screen. The deflection of the galvano- 

 meter due to the radiation from the ascending and heated carbonic acid being 

 now carefully neutralized by a constant source of heat radiating upon the 

 opposite face of the pile, a current of steam is made to ascend through an 

 iron tube passing vertically through the chauffer. Instantly the galvano- 

 meter deflects for heat much more powerfully than it did previously to its 

 compensation, when it was exposed to the full radiation from heated air and 

 carbonic acid. When the current of steam is interrupted, the needle imme- 

 diately returns to zero. If now a current of air be forced up the central 

 tube instead of steam, either no deflection at all, or a slight one for cold 

 occurs. The heat of the chauffer effectually prevents any condensation of 

 the steam. 



