Containing a Defcription of fuch INSTRUMENTS, PREPARATIONS, and EXPERIMENTS as explain and illuftrate the PowERS of ATTRACTION and REPULSION; the PROPERTIES of natural BODIES; the PRINCIPLES of Mechanic Arts; Chemical OPERATIONS; Nature of METEORS; Doctrine of VEGETATION; MAGNETISM, &c.

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HE Defign of this Course of Philofophy is to exhibit, in a very natural and eafy Manner, the principal and most important Phanomena or Appearances of natural Bodies; to account for their Caufes and Effects on plain and evident Principles;

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and to prove and illuftrate the fame by a great Variety of curious and new-contrived Inftruments and Experiments; fo as to render the whole not only the most rational and inftructive, but alfo the most pleasant and fatisfactory Entertainment.

2. The Subject of the prefent Lecture, are thofe Powers of Nature, which may be justly esteemed the fundamental Principles of Plate 1. all natural Philofophy; to fhew the Reality

of their Existence, their feveral Properties and wonderful Effects; and to apply the fame towards fettling a juft Theory of Chemistry, the Animal Oeconomy, Vegetation, the Nature of Meteors; together with the principal Properties of the Magnet, and its Use in Navigation.

3. This Power affects all the Particles of Matter, and acts upon them in a two-fold Manner, viz. 1. By caufing them to accede to, or approach each other; and because in this Refpect they seem to draw each other mutually, it is called the Power of Attraction. 2. By caufing thofe Particles, in fome Circumftances, to recede, or fly from each other, it is called Repulfion, or a centrifugal Force.

4. But this Power is in itself one and the Fig. 1. fame, and only acts in this different Manner in different Diftances between the Particles. Thus a Piece of Iron, touch'd with the Magnet, held near one End of a Magnetic Needle will attract it; but applied to the

other

other End, it will repel it. So the small Particles of Matter being nearly in Contact, ftrongly attract each other, and cohere together; but being feparated by the Action of Heat, or otherwife, they repel and fly from each other, as is evident by many Experi

ments.

5. Now to fhew that the Repulfion of one End of the Needle is not a Confequence of Attraction in the other, as fome pretend, I Fig. 2, take a Needle one half Brafs and the other Iron, and the fame End is repell'd in this as in the common Needle, which Experiment plainly fhews this Repulfion is real and pofitive between the two Bodies.

6. And further, it appears by Experiment, that the fame End of the Needle, which is repell'd in one Distance is attracted in another nearer Distance. And hence it follows, that there is a certain near Distance in which the Particles of Matter attract each other ; and which is therefore called the Sphere of Attraction; beyond which the said Power acts by Repulfion; and fo where Attraction ends there a repulfive Power commences.

7. This attracting Power may be con fider'd as affecting immediately the original Particles of Matter, and by that Means caufing them to adhere or cohere firmly together, and fo qualifying them to form larger Portions of Matter, or Bodies of different Degrees of B 2

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