HUMPHREYS: METE;0R0I.0GICAL PARADOXES 1 59 



TO WARM AIR, COOL IT 



This paradox is the converse of the one just discussed, and is 

 readily explained in much the same way. Referring again to 

 figure 2, let a mass of free air having the altitude and tempera- 

 ttu-e indicated by W in the figure, be cooled i ° C, or its position 

 shifted to C. It will at once become denser than it was, follow 

 the adiabatic gradient AB as it falls to lower levels, and, there- 

 fore, come to rest at the level and temperature indicated by 

 C, or at the intersection of the adiabatic gradient followed and 

 the existing gradient. That is, as a result of the initial cooling of 

 1° C, the given mass of air will fall 600 meters and become 

 5° C. warmer than it was before it was first cooled. In so far, 

 however, as the falling air gains heat from the surrounding 

 warmer atmosphere, it will come to rest at a correspondingly 

 greater elevation and lower temperature. 



This paradoxical phenomenon of warming by cooling is very 

 frequently and very prettily illustrated by the evening disap- 

 pearance of small detached clouds, such as alto- cumuli, fracto- 

 stratus, etc. As soon as the sun has set, these clouds and the air 

 masses they fill cool more rapidly than does the clear atmosphere. 

 They, therefore, fall to lower levels, warm up to higher tempera- 

 tures than they originally had, and evaporate. 



It will be interesting, in this connection, to note the logical 

 effect of a certain ingenious, often proposed, and at least once 

 experimentally tried, method of artificially inducing rainfall, 

 namely, the liberal sprinkling of a cloud mass with liquid air. 

 The result is, of course, an initial cooling of the cloud, followed, 

 as above explained, by a much greater warming. Instead of rain 

 being induced by this process, as its many inventors would con- 

 fidently expect, the chilled cloud is certain to grow warmer and 

 diminish in size, and, if considerably chilled may grow so much 

 warmer as to disappear entirely. Indeed, this particular liquid 

 air scheme is not a rain making process at all, but, on the contrary, 

 a rain deterrent! 



NOT AIR THAT IS HEATED, BUT AIR THAT IS NOT HEATED, 



IS THEREBY WARMED 



This particular paradox may suggest the superiority of "ab- 

 sent treatment;" nevertheless, it is perfectly sound. Heated 



