UOOK II. J APHORISMS. 479 



dissolved, are however softened. The same circumstance takes 

 place in sticks of wood, which become flexible when a little 

 heated in warm ashes. 



It is most readily observed in air, which instantly and mani 

 festly expands with a small decree of heat, as in Inst. 38, Tab. 3. 



It is also shown in the contrary nature of cold ; for cold con 

 tracts and narrows every substance;&quot; 1 so that in intense frosts 

 nails fall out of the wall and brass cracks, and heated glass 

 exposed suddenly to the cold cracks and breaks. So the air by a 

 slight decree 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 com 

 mon 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 anfi 

 dilating motion, but cold a contracting and condensing motion. 



II. The second difference is a modification of the preceding, 

 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 compound 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 dcsccnsum, which men 

 are wont to employ with delicate flowers, whose scent easily 

 evaporates. Their industry has devised placing the lire above 

 instead of below, that it may scorch less ; for not only flume 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 expansion 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, dipped 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. 



m To show the error of the text, we need only mention the case of 

 water, which, when confined in corked vases, and exposed to the action 

 of a freezing atmosphere, is sure to swell out and break those vessela 

 arhioh are not sufficiently large to contain its expanded volume. Megt 

 iotti narrates a hundred other instances of a similar character. Ed. 



