NOVUM ORGANUM. 123 



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 pre 

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

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

 upwards. 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 upwards. 



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 contrary nature of 

 cold ; whether its contraction be downwards, as the expan 

 sion of heat is upwards. Take therefore two iron rods or 

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

 little, and place a sponge, dipt in cold water, or some snow 

 below the one and above the other. We are of opinion 

 that the extremities will grow cold in that rod first where 

 it is placed beneath ; as the contrary takes place with regard 

 to heat. 



III. The third difference is this. That heat is not a 

 uniform expansive motion of the whole, but of the small 

 particles of the body ; and this motion being at the same 

 time restrained, repulsed, and reflected, becomes alternating, 

 perpetually hurrying, striving, struggling, and irritated by 

 the repercussion ; which is the source of the violence of 

 flame and heat. 



But this difference is chiefly shown in flame and boiling 

 liquids, which always hurry, swell, and subside again in 

 detached parts. 



It is also shown in bodies of such hard texture as not to 



