XI. The investigation of forms proceeds thus: a nature being given, we must first present to the understanding all the known instances which agree in the same nature, although the subject matter be considerably diversified. And this collection must be made as a mere history, and without any premature reflection, or too great degree of refinement. For instance; take the investigation of the form of heat.
Instances agreeing in the Form of Heat
- 1. The rays of the sun, particularly in summer, and at noon.
- 2. The same reflected and condensed, as between mountains, or along walls, and particularly in burning mirrors.
- 3. Ignited meteors.
- 4. Burning lightning.
- 5. Eruptions of flames from the cavities of mountains, etc.
- 6. Flame of every kind.
- 7. Ignited solids.
- 8. Natural warm baths.
- 9. Warm or heated liquids.
- 10. Warm vapors and smoke; and the air itself, which admits a most powerful and violent heat if confined, as in reverberating furnaces.
- 11. Damp hot weather, arising from the constitution of the air, without any reference to the time of the year.
- 12. Confined and subterraneous air in some caverns, particularly in winter.
- 13. All shaggy substances, as wool, the skins of animals, and the plumage of birds, contain some heat.
- 14. All bodies, both solid and liquid, dense and rare (as the air itself), placed near fire for any time.
- 15. Sparks arising from the violent percussion of flint and steel.
- 16. All bodies rubbed violently, as stone, wood, cloth, etc., so that rudders, and axles of wheels, sometimes catch fire, and the West Indians obtain fire by attrition.
- 17. Green and moist vegetable matter confined and rubbed together, as roses, peas in baskets; so hay, if it be damp when stacked, often catches fire.
- 18. Quicklime sprinkled with water.
- 19. Iron, when first dissolved by acids in a glass, and without any application to fire; the same of tin, but not so intensely.
- 20. Animals, particularly internally; although the heat is not perceivable by the touch in insects, on account of their small size.
- 21. Horse dung, and the like excrement from other animals, when fresh.
- 22. Strong oil of sulphur and of vitriol exhibit the operation of heat in burning linen.
- 23. As does the oil of marjoram, and like substances, in burning the bony substance of the teeth.
- [24.] Strong and well rectified spirits of wine exhibit the same effects; so that white of eggs when thrown into it grows hard and white, almost in the same manner as when boiled, and bread becomes burned and brown as if toasted.
- 25. Aromatic substances and warm plants, as the dracunculus [arum], old nasturtium, etc., which, though they be not warm to the touch (whether whole or pulverized), yet are discovered by the tongue and palate to be warm and almost burning when slightly masticated.
- 26. Strong vinegar and all acids, on any part of the body not clothed with the epidermis, as the eye, tongue, or any wounded part, or where the skin is removed, excite a pain differing but little from that produced by heat.
- 27. Even a severe and intense cold produces a sensation of
burning.[83]
- “Nec Boreæ penetrabile frigus adurit.”
- 28. Other instances.
We are wont to call this a table of existence and presence.
XII. We must next present to the understanding instances which do not admit of the given nature, for form (as we have observed) ought no less to be absent where the given nature is absent, than to be present where it is present. If, however, we were to examine every instance, our labor would be infinite.
Negatives, therefore, must be classed under the affirmatives, and the want of the given nature must be inquired into more particularly in objects which have a very close connection with those others in which it is present and manifest. And this we are wont to term a table of deviation or of absence in proximity.
Proximate Instances wanting the Nature of Heat
The rays of the moon, stars, and comets, are not found to be warm to the touch, nay, the severest cold has been observed to take place at the full of the moon. Yet the larger fixed stars are supposed to increase and render more intense the heat of the sun, as he approaches them, when the sun is in the sign of the Lion, for instance, and in the dog-days.[84]
The rays of the sun in what is called the middle region of the air give no heat, to account for which the commonly assigned reason is satisfactory; namely, that that region is neither sufficiently near to the body of the sun whence the rays emanate, nor to the earth whence they are reflected. And the fact is manifested by snow being perpetual on the tops of mountains, unless extremely lofty. But it is observed, on the other hand, by some, that at the Peak of Teneriffe, and also among the Andes of Peru, the tops of the mountains are free from snow, which only lies in the lower part as you ascend. Besides, the air on the summit of these mountains is found to be by no means cold, but only thin and sharp; so much so, that in the Andes it pricks and hurts the eyes from its extreme sharpness, and even excites the orifice of the stomach and produces vomiting. The ancients also observed, that the rarity of the air on the summit of Olympus was such, that those who ascended it were obliged to carry sponges moistened with vinegar and water, and to apply them now and then to their nostrils, as the air was not dense enough for their respiration; on the summit of which mountain it is also related, there reigned so great a serenity and calm, free from rain, snow, or wind, that the letters traced upon the ashes of the sacrifices on the altar of Jupiter, by the fingers of those who had offered them, would remain undisturbed till the next year. Those even, who at this day go to the top of the Peak of Teneriffe, walk by night and not in the daytime, and are advised and pressed by their guides, as soon as the sun rises, to make haste in their descent, on account of the danger (apparently arising from the rarity of the atmosphere), lest their breathing should be relaxed and suffocated.[85]