of three subdivisions into ministrations. 1. To the senses. 2. To the memory. 3. To the mind or reason. For we must first prepare as a foundation for the whole a complete and accurate natural and experimental history. We must not imagine or invent, but discover the acts and properties of nature.

But natural and experimental history is so varied and diffuse, that it confounds and distracts the understanding unless it be fixed and exhibited in due order. We must, therefore, form tables and coordinations of instances, upon such a plan, and in such order, that the understanding may be enabled to act upon them.

Even when this is done the understanding, left to itself and to its own operation, is incompetent and unfit to construct its axioms without direction and support. Our third ministration, therefore, must be true and legitimate induction, the very key of interpretation. We must begin, however, at the end, and go back again to the others.

11. 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, &c.

6. Flame of every kind.

7. Ignited solids.

8. Natural warm baths.

9. Warm or heated liquids.

10. Warm vapours 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, &c. 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. Quick lime 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 burnt and brown as if toasted.

25. Aromatic substances and warm plants as the dracunculus [arum], old nasturtium, &c.; 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.*

"Nam Boreæ penetrabile frigus adurit."

"Ne tenues pluviæ, rapidive potentia solis Acrior, aut Boreæ penetrabile frigus adurat." Virg. Georg. I. v. 92, 93.

28. Other instances.

We are wont to call this a table of existence and pre

sence.

12. 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 labour 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 connexion 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.

First negative subjunctive instance to the first affirmative instance. 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. Second negative to the second affirmative.

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 spunges moistened with vinegar and water, and to apply them now and then to their nostrils, as the air was not dense enough for their respira

tion; 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.

Third negative to the second affirmative.

The reflection of the solar rays in the polar regions is found to be weak and inefficient in producing heat; so that the Dutch, who wintered in Nova Zembla, and expected that their vessel would be freed about the beginning of July from the obstruction of the mass of ice which had blocked it up, were disappointed and obliged to embark in their boat. Hence the direct rays of the sun appear to have but little power even on the plain, and when reflected, unless they are multiplied and condensed, which takes place when the sun tends more to the perpendicular; for then the incidence of the rays occurs at more acute angles, so that the reflected rays are nearer to each other, whilst, on the contrary, when the sun is in a very oblique position, the angles of incidence are very obtuse and the reflected rays at a greater distance. In the mean time it must be observed, that there may be many operations of the solar rays, relating too to the nature of heat, which are not proportioned to our touch, so that, with regard to us, they do not tend to produce warmth, but, with regard to some other bodies, have their due effect in producing it.

Fourth negative to the second affirmative.

Let the following experiment be made. Take a lens the reverse of a burning glass, and place it between the hand and the solar rays, and observe whether it diminish the heat of the sun, as a burning glass increases it. For it is clear, with regard to the visual rays, that, in proportion as the lens is made of unequal thickness in the middle and at its sides, the images appear either more diffused or contracted. It should be seen, therefore, if the same be true with regard to heat.

Fifth negative to the second affirmative.

Let the experiment be well tried, whether the lunar rays

can be received and collected by the strongest and best burning glasses, so as to produce even the least degree of heat. But if that degree be, perhaps, so subtile and weak, as not to be perceived or ascertained by the touch, we must have recourse to those glasses which indicate the warm or cold state of the atmosphere, and let the lunar rays fall through the burning glass on the top of this thermometer, and then notice if the water be depressed by the heat.* Sixth negative to the second affirmative.

Let the burning glass be tried on warm objects which emit no luminous rays, as heated but not ignited iron or stone, or hot water, or the like; and observe whether the heat become increased and condensed, as happens with the solar rays.

Seventh negative to the second affirmative. Let it be tried on common flame.

Eighth negative to the third affirmative.

The effect of comets (if we can reckon them amongst meteors) in augmenting the heat of the season, is not found to be constant or clear, although droughts have generally been observed to follow them. However luminous lines, and pillars, and openings, and the like, appear more often in winter than in summer, and especially with the most intense cold but joined with drought. Lightning, and coruscations, and thunder, however, rarely happen in winter, and generally at the time of the greatest heats. The appearances we term falling stars are generally supposed to consist of some shining and enflamed viscous substance, rather than of violently hot matter. But let this be further

investigated.

Ninth negative to the fourth affirmative. Some coruscations emit light without burning; but are never accompanied by thunder.

Tenth negative to the fifth affirmative.

Eructations and eruptions of flame are to be found in cold climates as well as in hot, as in Iceland and Greenland; just as the trees of cold countries are sometimes inflammable and more pitchy and resinous, than in warm; as the fir, pine, and the like. But the position and nature of the soil, where such eruptions are wont to happen, is not

For the construction of Bacon's thermometer see No. 38 in the table of the degrees of heat. It serves also as a barometer, but is inaccurate in both capacities.