the limits prescribed to them by nature, or to raise water to a greater height, than the known weight or spring of the air can sustain. A notable example of this you have, in the fruitless endeavours of philosophers to perfect the refracting telescope, by grinding the glasses into various new figures, until sir Isaac Newton demonstrated that they were limited by another cause, than was suspected before, namely the different refrangibility of the rays of light, and not by the figure of the glasses. This discovery caused every optician and even sir Isaac Newton himself to despair of perfecting the refracting telescope, and set them upon the construction of reflectors, until another discovery, of the different refracting and dispersing powers of different kinds of glass, was made by Mr. Dolland, which has since enabled him to bring them to the wished for perfection.

But farther, it was no trifling discovery, that the contraction of the muscles of animals put their limbs in motion; though the original cause of that contraction remains still a secret: as it has given rise to many curious speculations on the force and dispositions of the muscles, and opened a wide prospect into the wisdom and goodness of the Creator discoverable in the animal economy. And the discovery, that the nerves have a considerable share in this action, leads us a step nearer to the original cause, gives us a more enlarged view of the subject, and affords considerable assistance in restoring this motion, when it is impaired, by pointing out the scat of the injuries to which it is exposed. Now to neglect all these discoveries, because we cannot advance farther, is plainly ridiculous.

Est aliquid prodire tenus, si non datur ultra. HoR.

B

It is acknowledged by all, that Galileo greatly improved philosophy by showing that the power which we call gravity, causes bodies to descend to the earth with an accelerated velocity, and to describe the curve, called a parabola, when projected forwards; yet we are ignorant of the cause of gravity, or what makes a body heavy. But although we are unacquainted with the secret spring of this power, we can estimate its effects, and derive many signal advantages, in the art of gunnery and the motion of spouting fluids, from the knowledge we have already obtained. Sir Isaac Newton has greatly increased our knowledge of the solar system, by demonstrating, upon indisputable geometrical principles, that this power of gravitation extends to the moon and to the most distant body in the solar system, regulating and determining all their complicated motions. As Galileo laid open the effects of this unknown power in the motion of bodies near the surface of the earth, more fully than any philosopher before his time; the towering genius of the incomparable Newton pursued it through all the planetary regions, nay to the most distant retreats of the flaming comets, and thereby exhibited the various intricacies of their motions to open view, which no astronomer from observation alone could ever have explained: as they never dreamt of the cause, and consequently never examined the principle, by which all their motions were governed.

Yet still we remain ignorant of the cause of gravitation, and cannot tell whether it be an essential property of all matter, or is only produced by the operation of some cause, which is hitherto undiscovered. But because the proper method of philosophizing, in the investigation of natural causes, requires that we

should not indulge groundless conjectures, but rather keep within the extent of our faculties, and be more ready to acknowledge their weakness than to conceal it. under the vain ostentation of hard names, occult qualities, and groundless hypotheses,-shall we therefore reject the evident advantages we have derived in geography, navigation and astronomy, merely because we are not able to account for the operation of this wonderful principle? No: rather let us thankfully receive the improvements that have been made, and proceed with the same caution and circumspection, in the investi: gation of the hidden powers of nature, which has enabled others, and particularly the prince of philosophers, the great sir Isaac Newton, to make such amazing progress in the knowledge of nature.

Although from his accurate observations, sir Isaac Newton found reason to conclude that gravitation was a universal property belonging to all the perceptible bodies in the universe, and to every particle of matter; yet he nowhere asserts this property to be essential, but on the contrary has given some hints as to the cause of it; which he has left for the investigation of others. It is extremely difficult to determine what properties are essential to matter, and what depend upon the frame and composition of bodies alone: what properties belong to every particle of matter however altered and changed by composition or dissolution, and what only arise from the union and composition of these particles with other portions of matter. And since we have no other method of making discoveries in philosophy, but by gradual inquiries into nature, we must first admit all the properties we observe, and then endeavour carefully to distinguish between those, wherewith the very substances themselves are in

dued, and those, which only exist in appearance; while this appearance at the same time depends upon the structure of compound bodies. And we must never forget that as some of the properties of matter have been gradually discovered from time to time, more of them may yet be found out, by the researches of future philosophers; and that possibly we are not provided with sufficient methods of perception, to discover them all. But still, whatever properties occur, whose existence we have fully and clearly proved, are to be considered as the proper objects of natural philosophy; the design of which is to explain the various phenomena of the natural world. And it is the business of the philosopher, by the most accurate and careful methods in his power, to distinguish between those, that are original and essential to every particle of matter, and those, that may be derived from the operation of some more remote cause, perhaps yet unknown to him and the world.

In this method, we shall endeavour to conduct your inquiries into the laws of nature; and give you such solutions of the various phenomena, that we observe in the material world, as have been generally received by philosophers of the most approved characters; requesting you, in the mean time, to admit of no solution, but what appears to be founded on the established principles and properties of matter, and sufficiently confirmed, by an adequate number of observations and experiments. And although we shall meet with many phenomena in this extensive science, which we are yet unable to explain; yet we hope to lay before you the first principles of natural philosophy, and to give you so many solutions, in its various branches, as will be sufficient to open to your view the conduct

of nature in her leading operations; to give you a relish for philosophical inquiries; and to excite that thirst for farther investigations; by which a foundation may be laid, for your future additions to the stock of general knowledge, and your acquiring the singular honour of becoming the patrons of science, the ornaments of the republic of letters, and the benefactors of mankind.

And there is ample room for the exercise of the most penetrating genius, and unwearied application. There is more in a single vegetable, than has yet been adequately accounted for by the ablest philosopher that ever lived. And when you survey the extensive fields of useful knowledge, which are opening to your investigation, through the unexplored deserts of this new world, and the improvements that are daily making by the sons of science, you must naturally feel your hearts swell with an honest and laudable ambition, to distinguish yourselves amongst the most celebrated inventors of those useful arts, which have a tendency to embellish and exalt the understanding, alleviate the miseries of human nature, and promote the happiness of mankind. Animated with this expectation, I cannot but promise myself your patient and candid attention; and I shall account myself happy, if I shall be able, in the course of these lectures, to contribute any thing to the republic of letters, in your future advancement and distinction in the world.