incompetent and unfit to form axioms, unless it be directed and guarded. Therefore in the third place we must use Induction, true and legitimate induction, which is the very key of interpretation. But of this, which is the last, I must speak first, and then go back to the other ministrations. XI. The investigation of Forms proceeds thus: a nature being given, we must first of all have a muster or presentation before the understanding of all known instances which agree in the same nature, though in substances the most unlike. And such collection must be made in the manner of a history, without premature speculation, or any great amount of subtlety. For example, let the investigation be into the Form of Heat. Instances Agreeing in the Nature of Heat. 1. The rays of the sun, especially in summer and at noon. 2. The rays of the sun reflected and condensed, as between mountains, or on walls, and most of all in burning-glasses and mirrors. 3. Fiery meteors. 4. Burning thunderbolts. 5. Eruptions of flame from the cavities of moun tains. 6. All flame. 7. Ignited solids. 8. Natural warm-baths. 9. Liquids boiling or heated. 10. Hot vapours and fumes, and the air itself, which conceives the most powerful and glowing heat, if confined; as in reverbatory furnaces. 11. Certain seasons that are fine and cloudless by the constitution of the air itself, without regard to the time of year. 12. Air confined and underground in some caverns, especially in winter. 13. All villous substances, as wool, skins of animals, and down of birds, have heat. 14. All bodies, whether solid or liquid, whether dense or rare (as the air itself is), held for a time near the fire. 15. Sparks struck from flint and steel by strong percussion. 16. All bodies rubbed violently, as stone, wood, cloth, &c., insomuch that poles and axles of wheels sometimes catch fire; and the way they kindled fire in the West Indies was by attrition. 17. Green and moist vegetables confined and bruised together, as roses packed in baskets; insomuch that hay, if damp when stacked, often catches fire. 18. Quick lime sprinkled with water. 19. Iron, when first dissolved by strong waters in glass, and that without being put near the fire. And in like manner tin, &c., but not with equal intensity. 20. Animals, especially and at all times internally; though in insects the heat is not perceptible to the touch by reason of the smallness of their size. 21. Horse-dung and like excrements of animals when fresh. 22. Strong oil of sulphur and of vitriol has the effect of heat in burning linen. 23. Oil of marjoram and similar oils have the effect of heat in burning the bones of the teeth. 24. Strong and well rectified spirit of wine has the effect of heat; insomuch that the white of an egg being put into it hardens and whitens almost as if it were boiled; and bread thrown in becomes dry and crusted like toast. 25. Aromatic and hot herbs, as dracunculus, nasturtium vetus, &c., although not warm to the hand (either whole or in powder), yet to the tongue and palate, being a little masticated, they feel hot and burning. 26. Strong vinegar, and all acids, on all parts of the body where there is no epidermis, as the eye, tongue; or on any part when wounded and laid bare of the skin; produce a pain but little differing from that which is created by heat. 27. Even keen and intense cold produces a kind of sensation of burning; Nec Boreæ penetrabile frigus adurit.1 28. Other instances. This table I call the Table of Essence and Presence. XII. Secondly, we must make a presentation to the understanding of instances in which the given nature is wanting; because the Form, as stated above, ought no less to be absent when the given nature is absent, than present when it is present. But to note all these would be endless. The negatives should therefore be subjoined to the affirmatives, and the absence of the given nature in1 Nor burns the sharp cold of the northern blast. in those subjects only that are most akin to ers in which it is present and forthcoming. This I can the Table of Deviation, or of Absence in Proximity. in Proximity where the Nature of Heat is Absent. 1. The rays of the moon and of stars and comets are not found to be hot to the touch; indeed the severest colds are observed to be at the full moons. The larger fixed stars however, when passed or approached by the sun, are supposed to increase and give intensity to the heat of the sun; as is the case when the sun is in the sign Leo, and in the Dog-days. To the 2nd. 2. The rays of the sun in what is called the middle region of the air do not give heat; for which there is commonly assigned not a bad reason, viz. that that region is neither near enough to the body of the sun from which the rays emanate, nor to the earth from which they are reflected. And this appears om the fact that on the tops of mountains, unless they are very high, there is perpetual snow. On the other band it has been observed that on the peak of Teneriffe, among the Andes of Peru, the very tops of the tains are free from snow; which lies only some» at lower down. Moreover the air itself at the very y found to be by no means cold, but only rare and 2 insomuch that on the Andes it pricks and hurts the eyes by its excessive keenness, and also irritates the of the stomach, producing vomiting. And it served by the ancients that on the top of Olymrarity of the air was such that those who asit had to carry sponges with them dipped in vinegar and water, and to apply them from time to time to their mouth and nose, the air being from its rarity not sufficient to support respiration; and it was further stated that on this summit the air was so serene, and so free from rain and snow and wind, that letters traced by the finger in the ashes of the sacrifices on the altar of Jupiter remained there till the next year without being at all disturbed. And at this day travellers ascending to the top of the Peak of Teneriffe make the ascent by night and not by day; and soon after the rising of the sun are warned and urged by their guides to come down without delay, on account of the danger they run lest the animal spirits should swoon and be suffocated by the tenuity of the air. To the 2nd. 3. The reflexion of the rays of the sun in regions near the polar circles is found to be very weak and ineffective in producing heat; insomuch that the Dutch who wintered in Nova Zembla, and expected their ship to be freed from the obstructions of the mass of ice which hemmed her in by the beginning of July, were disappointed of their expectation, and obliged to take to their boat. Thus the direct rays of the sun seem to have but little power, even on the level ground; nor have the reflex much, unless they are multiplied and combined; which is the case when the sun tends more to the perpendicular; for then the incident rays make acuter angles, so that the lines of the rays are nearer each other; whereas on the contrary, when the sun shines very obliquely, the angles are very obtuse, and thus the lines of rays are at a greater distance from each other. Meanwhile it should be observed that there may be many operations of the sun, and those too depending on the nature of heat, which are not propor |