NOVUM ORGANUM. 



by putting a stick, or something of the kind, into flame, to see whether 

 it be not burned more quickly at the sides than in the middle of the 

 llame. 



37. Now there are very many degrees in susceptibility of heat ; and, 

 first of all, it must be remarked how small and trifling a heat changes, 

 and to a certain degree warms, even those bodies which are least 

 susceptible of it. For the heat of the hand imparts some heat to a 

 bullet of lead or any other metal, when it has been held in it a little 

 while. So easily and universally is heat transmitted and excited, 

 without the body undergoing any apparent change. 



38. Air takes up and gives oflf heat more easily than any other body 

 known to us, as is best seen in heat glasses. They are constructed 

 thus : take a glass with a hollow belly, and a long narrow neck ; turn 

 it upside down, and insert it, mouth downwards and belly upwards, 

 into another glass vessel containing water, so that the mouth of the 

 upper vessel touches the bottom of the receiver ; let the neck of the 

 inserted glass rest a little on the mouth of the receiver, so that it may 

 stand steadily ; and that this may be done more conveniently, apply a 

 little wax to the mouth of the receiver, taking care not to close it 

 entirely, lest the motion, of which we are now about to speak, and 

 which is very subtle and delicate, be impeded for want of a supply of air. 



Now the inverted glass, before it is introduced into the other, should 

 have its upper part, ;&amp;gt;., its belly, heated at the fire. Then, when the 

 heated glass has been placed as we have directed, the air ( which was 

 expanded by the heat) will draw itself back and contract (after a delay 

 sufficient to allow for the extinction of the adventitious heat) to the 

 same extension or dimension as that of the surrounding air at the time 

 of the insertion of the glass, and will draw up the water to a corre 

 sponding standard. Moreover there should be attached along narrow 

 slip of paper, graduated at pleasure. Then you will see that, as the 

 temperature of the day rises with heat, or falls with cold, the air 

 contracts in like manner ; and this will be rendered conspicuous by 

 the ascent of the water when the air is contracted, and by its descent 

 or depression when it is dilated. Now the sensibility of air to heat 

 and cold is so subtle and exquisite, as far to exceed the power of 

 human touch ; so that a ray of sunlight, or the heat of the breath, 

 and, much more, the heat of the hand, falling on the top of the glass, 

 immediately depresses the water to a perceptible degree. But yet we 

 think that the spirit of animals has a still more exquisite sense of heat 

 and cold, only that it is hindered and rendered dull by the mass of 

 their bodies. 



39. Next to air we think that those bodies are most sensitive of heat 

 which have been recently changed and compressed by cold, such as 

 snow and ice, for they begin to be dissolved and liquefied by any 

 gentle warmth. Next to them probably comes quicksilver; after this 

 come fatty bodies, such as oil, butter, and the like ; then wood, then 

 water. Lastly, stones and metals, which do not readily admit of heat, 

 especially internally. These, however, when they have once acquired 

 Jieat, retain it for a very long time ; so that if brick or stone, or iron 



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