3rd negative to the 2nd affirmative.

4th negative to the 2nd affirmative.

nostrils, as the Air was not dense enough for their respi-
ration; on the Summit of which mountain it is also related,
there reigned so great a serenity and calm, free from rain,
show, 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 day-time,
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.

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 pro-
portioned 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.

Let the following Experiment be made. Take a lens the reverse of a Burning Glass, and place it between the

4

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.

to the 2nd

Let the Experiment be well tried, whether the Lunar 5th negative Rays can be received and collected by the strongest and affirmative. 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.1

to the 2nd affirmative.

Let the Burning Glass be tried on Warm Objects which 6th negative 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.

Let it be tried on common flame.

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.

1 For the construction of Bacon's Thermometer see No. 38 in the tables of the degrees of Heat. It serves also as a Barometer, but is inaccurate in both capacities.

7th negative to the 2nd affirmative. 8th negative affirmative.

to the 3rd

oth negative to the 4th affirmative.

1oth nega tive to the

The appearances we term Falling Stars are generally sup-posed to consist of some shining and inflamed viscous substance, rather than of violently hot matter. But let this

be further investigated.

Some Coruscations emit Light without burning; but are never accompanied by Thunder.

Eructations and eruptions of Flame are to be found in 5th affirma cold Climates as well as in hot, as in Iceland and Greenland ;.

tive.

11th nega

tive to the 6th affirma

tive.

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 yet sufficiently investigated to enable us to subjoin a Negative · instance to the Affirmative.

All flame is constantly more or less warm, and this instance is not altogether Negative. Yet it is said that the Ignis Fatuus (as it is called), and which sometimes is driven against walls, has but little heat; perhaps it resembles that of spirits of wine, which is mild and gentle. That flame, however, appears yet milder, which in some well authenticated and serious Histories, is said to have appeared round the head and hair of Boys and Virgins, and instead of burning their hair, merely to have played about it. And it is most certain that a sort of Flash, without any evident heat, has sometimes been seen about a Horse when sweating at night, or in damp weather. It is also a well known fact,' and it was almost considered as a miracle, that a few years since a Girl's Apron sparkled when a little shaken or rubbed; which was perhaps occasioned by the alum or salts with which the apron was imbued, and which after having been stuck together and incrusted rather strongly were broken by the friction. It is well known that all Sugar, whether Candied or plain, if it be hard, will sparkle when broken or Was it a Silk Apron which exhibited electric Sparks? Silk was.

then scarce.

scraped in the dark. In like manner Sea and Salt Water is
sometimes found to shine at night when struck violently by
the oar.
The Foam of the Sea when agitated by tempests
also Sparkles at night, and the Spaniards call this appear-
ance the Sea's lungs. It has not been sufficiently ascertained
what degree of heat attends the Flame which the Ancient
Sailors called Castor and Pollux, and the moderns call St.
Ermu's Fire.

Every Ignited Body that is red-hot is always Warm, although without flame, nor is any Negative instance subjoined to this Affirmative. Rotten Wood, however, approaches nearly to it, for it shines at night, and yet is not found to be warm; and the putrefying scales of Fish which shine in the same manner are not warm to the touch, nor the body of the Glowworm, or of the Fly called Lucciola.1

The situation and nature of the Soil of natural warm Baths has not been sufficiently investigated, and therefore a Negative instance is not subjoined.

To the instances of warm Liquids we may subjoin the Negative one of the peculiar nature of Liquids in general. For no tangible liquid is known that is at once warm in its nature and constantly continues Warm; but their Heat is only superinduced as an adventitious Nature for a limited time; so that those which are extremely Warm in their power and effect, as spirits of Wine, chymical aromatic oils, the oils of vitriol and sulphur, and the like, and which speedily burn, are yet cold at first to the touch, and the water of natural Baths, poured into any vessel and separated from its source, cools down like water heated by the fire. It is however true that Oily Substances are rather less cold to the touch than those that are Aqueous, Oil for instance than Water, Silk than Linen; but this belongs to the Table of Degrees of Cold.

1 The Italian Fire-Fly.

15th nega tive to the 10th affirmative.

16th nega.

tive to the 10th affirmative.

17th nega

tive to the 11th affirmative.

18th nega. tive to the 12th affirmative.

In like manner we may subjoin a Negative instance to that of warm Vapour, derived from the nature of Vapour itself; as far as we are acquainted with it. For exhalations from Oily Substances, though easily inflammable, are yet never warm unless recently exhaled from some warm substance.

The same may be said of the instance of Air. For we never perceive that Air is warm unless confined or pressed, or manifestly heated by the Sun, by Fire, or some other warm body.

A Negative instance is exhibited in Weather by its coldness with an East or North Wind, beyond what the Season would lead us to expect; just as the contrary takes place with the South or West winds. An inclination to rain (especially in winter) attends warm weather, and to Frost, cold weather.

A Negative instance as to Air confined in caverns may be observed in summer. Indeed we should make a more diligent inquiry into the nature of confined Air. For in the first place the qualities of Air in its own nature with regard to Heat and Cold, may reasonably be the subject of doubt. For Air evidently derives its Heat from the effects of Celestial Bodies, and possibly its Cold from the exhalation of the Earth, and in the Mid Region of Air (as it is termed) from cold vapours and snow, so that no judgment can be formed of the nature of Air by that which is out of doors and exposed, but a more correct one might be derived from confined Air. It is necessary, however, that the Air should be enclosed in a vessel of such materials as would not imbue it with heat or cold of themselves, nor easily admit the influence of the external Atmosphere. The Experiment should be made therefore with an earthen jar, covered with folds of leather to protect it from the external Air, and the air should be kept three or four days in this vessel well closed. On opening the jar, the degree of heat may be