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its source, cools down like water heated by the fire. It is, 

 however, true that oily substances are rather less cold to 

 the touch than those that are aqueous, oil for instance than 

 water, silk than linen ; but this belongs to the table of de 

 grees of cold. 



In like manner we may subjoin a negative instance to 

 that of warm vapor, derived from the nature of vapor itself, 

 as far as we are acquainted with it. For exhalations from 

 oily substances, though easily inflammable, are yet never 

 warm unless recently exhaled from some warm substance. 



The same may be said of the instance of air; for we 

 never perceive that air is warm unless confined or pressed, 

 or manifestly heated by the sun, by fire, or some other 

 warm body. 



A negative instance is exhibited in weather by its cold 

 ness with an east or north wind, beyond what the season 

 would lead us to expect, just as the contrary takes place 

 with the south or west winds. An inclination to rain (espe 

 cially in winter) attends warm weather, and to frost cold 

 weather. 



A negative instance as to air confined in caverns may be 

 observed in summer. Indeed, we should make a more dili 

 gent inquiry into the nature of confined air. For in the first 

 place the qualities of air in its own nature with regard to 

 heat and cold may reasonably be the subject of doubt; for 

 air evidently derives its heat from the effects of celestial 

 bodies, and possibly its cold from the exhalation of the 

 earth, and in the mid region of air (as it is termed) from 

 cold vapors and snow, so that no judgment can be formed 

 of the nature of air by that which is out of doors and ex 

 posed, but a more correct one might be derived from con 

 fined air. It is necessary, however, that the air should be 



