NOVUM ORGANUM. 327 



It is shown also in iron or stones, which, although not liquefied or 

 fused, are yet softened. This is also the case with wooden sticks, 

 which become flexible when heated for a short time in hot ashes. 



But that motion is best seen in the case of air, which continuously 

 and manifestly dilates with a slight heat ; as is seen from Instance 38, 

 Table 3. 



It is shown also in the contrary Nature of Cold. For cold contracts 

 all bodies, and forces them into a narrower space ; so that during 

 intense cold nails fall out of the walls, brazen vessels split, and glass, 

 when heated and suddenly placed in the cold, cracks and breaks. In 

 like manner, air is contracted by slight chills, as is seen from Instance 

 38, Table 3. But of this we shall speak more at large in our inquiry 

 concerning cold. 



Nor is it wonderful that heat and cold exhibit very many actions in 

 common (for which see Instance 32, Table 2), when two of the follow 

 ing Differences (of which we shall speak presently) are found to suit 

 either Nature ; though in the Difference (of which we are now speak 

 ing) their actions are diametrically opposed. For heat gives an 

 expansive and dilating, cold a contracting and combining motion. 



The Second Difference is a modification of the first, viz. that heat is 

 a motion expansive (or tending towards the circumference), but with 

 this condition, that the body tends upwards with it. For without doubt 

 there are very many kinds of mixed motion ; e.g., an arrow or a dart 

 rotates at the same time that it proceeds, and proceeds as it rotates. 

 In like manner, the motion of heat is at once an expansive motion and 

 a motion upwards. 



And this Difference is shown by putting a pair of tongs or an iron 

 rod into the fire ; for if it be inserted perpendicularly, and held by the 

 top, it quickly burns the hand ; but if horizontally, or from below, 

 much more slowly. 



It is also conspicuous in distillation pco descensorium^ which is used 

 for the more delicate flowers, the scent of which easily escapes. For 

 industry has discovered the plan of placing the fire above instead of 

 below, that it may burn less. For not only flame tends upwards, but 

 all heat also. 



Now, let an experiment be made with regard to this fact on the 

 contrary Nature of Cold, viz. whether cold does not contract a body 

 in a downward, just as heat dilates it in an upward direction. Take, 

 therefore, two iron rods or tubes of glass, alike in all respects ; heat 

 them a little, and then place a sponge full of cold water or a lump of 

 snow under the one, and the same above the other. For we think 

 that refrigeration will take place more quickly at the extremities of 

 that stick upon which the snow is placed than at those of that under 

 which it is placed ; the reverse of which is the case with heat. 



The Third Difference is this : that heat is motion of expansion, not 

 uniformly of the whole body, but in its lesser particles ; and at the 

 same time restrained, repelled, and turned back, so that it assumes a 



