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the air, by a slight degree of cold, contracts itself, as in 

 Inst. 38, Tab. 3. More will be said of this in the inquiry 

 into cold. 



Nor is it to be wondered at if cold and heat exhibit many 

 common effects (for which see Inst. 32, Tab. 2), since two 

 differences, of which we shall presently speak, belong to 

 each nature: although in the present difference the effects 

 be diametrically opposed to each other. For heat occasions 

 an expansive and dilating motion, but cold a contracting and 

 condensing motion. 



II. The second difference is a modification of the preced 

 ing, namely, that heat is an expansive motion, tending 

 toward the exterior, but at the same time bearing the body 

 upward. For there is no doubt that there be many com 

 pound motions, as an arrow or dart, for instance, has both 

 a rotatory and progressive motion. In the same way the 

 motion of heat is both expansive and tending upward. 



This difference is shown by putting the tongs or poker 

 into the fire. If placed perpendicularly with the hand 

 above, they soon burn it, but much less speedily if the 

 hand hold them sloping or from below. 



It is also conspicuous in distillations per descensum, which 

 men are wont to employ with delicate flowers, whose scent 

 easily evaporates. Their industry has devised placing the 

 fire above instead of below, that it may scorch less ; for not 

 only flame but all heat has an upward tendency. 



Let an experiment be made on the tontrary nature of 

 cold, whether its contraction be downward, as the expansion 

 of heat is upward. Take, therefore, two iron rods or two 

 glass tubes, alike in other respects, and warm them a little, 

 and place a sponge, dipped in cold water, or some snow, be 

 low the one and above the other. We are of opinion that 



