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principle at last fubfides; yet the tenacity of the fluid fhall detain it a long time, perhaps for fome years, as may appear from inftances mentioned in other parts of thefe Lectures. And further add to all this MOTION, and the ability of fluids to fupport fpecifically heavier bodics is ftill increafed, as well as the ability to immerge light bodies: By this it is, that duft in windy weather is raised in the air, that mud floats in rivers and lakes, and hereby many phænomena of extraordinary confequence are occafioned.

In this lecture have been confidered and demonftrated, two univerfal properties of matter, and the diftinction of matter into four elements, and the compofition of each. In the following lecture, the properties of each element fhall be more particularly confidered and demonftrated, and the phænomena which shall make the foundation of reasoning, shall be rather thofe of the common than the rare kind: For although rarity ftrikes the mind more, yet it informs it lefs. When this fhall be done, as is hoped, with a good degree of fatisfaction; fome phænomena of the rare kind fhall be laid before you, and the laws of matter previously demonstrated shall be applied to them.

Having thus finished the mathematical part of our defign, which tho' not of the marrow, but rather the furface of that fcience, is fitter for a reader than a hearer; as indeed every thing in that science is; a favour must be requested of all thofe, who perufe these matters with attention, not to reject the truth or cenfure the whole, if any error in the numbers &c. may have flipt from the pen. Great men have erred, and the main tendency of their writings has not been deftroyed thereby. The ingenious Borelli thought he had demonftrated, the force of the heart to protrude the blood, to be equal to 180000lb. Yet the accurate James Keil has fince demonftrated that the force of 1lb. will protrude 100lb. of blood. A Borello quidem ponderi 180000 librarum æqualis in corde vis, quæ viginti libras fanguinis moveret, defiderabatur: Sed ex fupra ⚫ demonftratis patet, centum libras fanguinis, à vi cordis non unam libram ⚫ excedente, moveri poffe. Hoc nonnullis aut procul intuentibus, aut parum cogitantibus mirum fortaffe videri poteft; quod fi hane rem propriùs et penitiùs infpiciamus, nihil huic vi cordis attributum inveniemus, quod non abunde poteft præftare.' Keil Tent. med.

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In the fame manner, others have erred, and yet preserve an eminent fame: That therefore which the most ingenious can not avoid, is pardonable in all.

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ΡΗ ΑΝΟΜΕΝΑ.

LECTURE II.

Nature has an univerfal principle for each class of things, and therefore the contemplation of all natural things conduces to the knowledge of a particular one; fo, from a fcientifical knowledge of any one, does follow the fame of all and every one. See Hook his defcription of experiments on Lignum Foffile, page 106.

No man can advantageously discover the nature of any thing, in that thing itself, but the INQUIRY must be extended to matters that are more common.

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Lord Verulam his new Machine. Aph. 70.

1

LECTURE II.

I

N the former lecture, the four elements having been confidered as mixt bodies; in this, the properties of each fhall be particularly laid down, upon the fame confideration of their being mixt bodies.

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the phænomena applied to this purpose, shall be for the most part fuch as are most commonly to be obferved, meaning to treat the fubject popularly; yet with ftrict regard to truth in the laws of Nature: Ånd whereas our defign is to haften to the main purpose, to wit, the application of demonftrated properties of matter, to particular phænomena, the demonstrations shall be as fhort, but as clear as poffible.

The element which feems to have the nearest relation to animal and vegetable life, fhall be firft treated of.

AIR is an elaftic fluid, incompaffing this globe of earth, and pervading it, capable of a great degree of expanfion and condensation, and of a great increase of elasticity and diminution of it. It is a principle of the prefervation of life in all living animals and vegetables, and a principle of putrefaction and corruption in them, when they are dead. It abounds with all forts of matter, and holds perpetual commerce with this our globe, in receiving exhalations pregnant with particles of various kinds, and forming dew, rain, hail, froft and fnow. It will be proper to treat thefe in diftinct propofitions.

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Air is an elastic fluid capable of a great degree of expansion and condensation, and of a great increase of clafticity and diminution of it.

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DEMONSTRATION.

Air fuddenly expanded by the means of gunpowder fired, is capable of giving a vast force to engins of war; and fire in the bowels of the earth fhall fo rarify it, that it fhall produce earthquakes, burft the furface, and throw out immenfe quantities of matter with fuch rumbling founds, as terrify mankind. Animals fuddenly immerfed in water to great depths, by means of diving bells, shall be compreffed to death by the condensation of the air furrounding them; and if they be gradually immersed so as to take in the dense air without deftruction, and be fuddenly raised to the thin atmosphere above the water, they shall burst by means of the denfe air within expanding itself. The deftruction, or even diminution of the elasticity of the air, is not obferved in the fedentary air fometimes found in vaults, and large oyl jars, which have been many years empty of oyl, and lie in clofe places; nor in fome kinds of damps in mines, although they are known to destroy life, and extinguish fire, as air paffing through a tube from one fire to another will extinguifh it, and air paffing through the lungs of any animal, becomes unfit for refpiration. In public affemblies where there is not allowed a free paffage for the air, the air that is confined having been once breathed, will extinguifh the candles, occafion fainting, and the hazard of life.

All those phænomena are not owing to the diminution of the elasticity of the air. For by experiment fuch air has been found equally elaftic with wholfome air. There is therefore fome other quality neceffary to be found in air, in order to preferve life and fire, befides elafticity; but in this propofition, we are to confider only the increase and diminution of clafticity in that element. By condensing air, it is rendered more claftic, and by thinning, lefs fo; yet the action of thinning, fhall produce the fame effect with that of condenfation in fome inftances, and be of equal force. A ball A ball may be discharged from a gun, by means of air condenfed by an engin for that purpofe, with equal force with a ball discharged by rarified air, arifing from inflamed gunpowder. Yet when air is once expanded by heat, and any quantity of it poffeffing a certain space, is compared with that of condenfed air, poffeffing an equal fpace, the former

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