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LECTURES.

NATURAL experimental philosophy is a science, which investigates the reason and causes of the various phenomena which occur in the material world, and makes the truth of the solutions given, evident to the senses, by plain and adequate experiments.

By the phenomena of nature, we mean all the situations, motions, and appearances of natural bodies, which are evident to the senses, and not immediately dependent upon the voluntary agency of an intelligent being; by which we do not exclude those appearances, which are found in animal bodies, so far as they do not depend upon the volition of the animal, but arise by the instrumentality of second causes. All these situations and motions are produced by certain fixed and determinate rules, which are denominated the laws of nature; as they are the invariable appointment of the First Cause of all things, whereby he determined that certain natural causes should always, in the same circumstances, invariably produce the same effects. And in the production of the effect, they constantly observe this fundamental rule: that the effect shall be always proportionable to the whole power and effi ciency of the cause. Thus the same quantity of fire always burns, by a natural necessity, with the same degree of intensity; and gravitation always causes a

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LECTURES.

NATURAL experimental philosophy is a science, which investigates the reason and causes of the various phenomena which occur in the material world, and makes the truth of the solutions given, evident to the senses, by plain and adequate experiments.

By the phenomena of nature, we mean all the situations, motions, and appearances of natural bodies, which are evident to the senses, and not immediately dependent upon the voluntary agency of an intelligent being; by which we do not exclude those appearances, which are found in animal bodies, so far as they do not depend upon the volition of the animal, but arise by the instrumentality of second causes. All these situations and motions are produced by certain fixed and determinate rules, which are denominated the laws of nature; as they are the invariable appointment of the First Cause of all things, whereby he determined that certain natural causes should always, in the same circumstances, invariably produce the same effects. And in the production of the effect, they constantly observe this fundamental rule: that the effect shall be always proportionable to the whole power and efficiency of the cause. Thus the same quantity of fire always burns, by a natural necessity, with the same degree of intensity; and gravitation always causes a

heavy body to descend from a given height with the same invariable force. In this consists the difference between a natural and an intelligent cause: as the latter may produce its effects, very much disproportioned to the whole of its power. Thus a man may raise a greater or less weight, just as he pleases. The one, acting with evident design, may alter, increase, or lessen the effect at pleasure; but the other, acting without design, has no such power to alter the effects produced. It is from this invariable proportion between the cause and the effect in natural agents that we estimate the force of the cause, from the known quantity of the effect, and vice versa; and therefore it should be carefully observed, as we shall have frequent occasion for it, in our subsequent lectures, while we endeavour to investigate and ascertain the cause of any particular effect from the established proportion that must subsist between them.

In the investigation of the laws of nature, many philosophers proceeded upon false and sophistical principles, until the incomparable Newton appeared, and laid down the few following rules of philosophizing; which are so plain and solid, as to gain the approbation of every intelligent person, who desires to make any safe progress in the knowledge of nature.

1. That no more causes are to be admitted, than what are true and sufficient to explain the phenomena. A variety of causes, to produce the same effect, is needless, and therefore cannot be supposed to take place, in the workmanship of Him, who does nothing in vain. As we have no safe method of investigating any cause, but by its known effects; when one cause is sufficient to explain the phenomena, we have no possible means of knowing that there are two or more;

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