The eagerness with which you desire to know the use of this apparatus will be considerably heightened, when I acquaint you with the purposes for which it is designed. It is intended to introduce you to natural philosophy, to enrich your minds with the knowledge acquired by the labours of the great and wise men who lived before you, to make you acquainted with the scenery of nature, the ways and means made use of by the great author and supporter of your being and mine, in producing those wonderful appearances you see in the air, the changes you observe in the seasons, the nature of the air you breathe, and the fire which animates your frame. But this apparatus is not confined merely to an explanation of the operations of God in nature; it will instruct you also in the wisdom he has communicated to man, and shew you the nature of those engines which they have contrived, the action of that useful instrument the common pump will be explained, and you will learn to know when they are well or ill constructed. You will comprehend the properties and principles of the steam engine, whose operations have so often excited your admiration; it will be too tedious to enumerate all the advantages you may acquire from this apparatus. Let me assure you that explaining them to your companions, and performing the operations yourselves, will not be one of the least, for by thus exerting the faculties of body and mind, both will be strengthened and improved.

From natural philosophy you will learn that the Creation is but an image or picture of the divine perfection and therefore bears a character of his infinity and immensity: that this small part of it which we inhabit, is but a point in comparison of the solar system: that the solar system is but a point in comparison of the vast regions of the fixed stars: that these superior regions themselves are but a point in comparison of the innumerable worlds that lie perhaps hid in the bosom of immensity: that in this point which we inhabit, we know only some superficial qualities and properties of nature: that, as Sir Isaac Newton said, all the discoveries mortals can make are like those of a child upon the borders of the sea, who has only broken some pebbles, and opened some shells, to see what is in them, while there lies beyond him a boundless ocean, of which he has no ideas: that we can never be true philosophers till we see the AUTHOR of nature face to face; compare the pictures with their original; and know, by direct intuition, their mutual relation and resemblances. Lord Bacon terms natural philosophy, the great mother of the sciences, for neither the arts of speech, logic, medicine, civil policy, morality, religion, &c. can be advantageously exercised, improved, understood, or instituted without it, and all the mechanical sciences depend upon it. […]

Not to detain you longer from an examination of the articles before you, I shall first give you a general description of some of them, and tell you their several names; this will render the explanation of their respective uses easier and more simple, and will enable you to make experiments with them, and explain their effects with greater facility.

The instrument before you is called an air-pump. It is one of the most useful of all of those philosophical instruments whose action depends on the air. It consists of a pump or syringe, annexed by means of other pieces to a glass vessel, and is so contrived that by moving a rod up and down, the air contained in the receiver may be extracted. It is formed of five principal parts: 1. The barrel. 2. The piston moveable in the barrel. 3. Two valves or openings so contrived as to prevent the air returning back again. 4. The plate of the pump on which the vessels are to be placed, that the air may be extracted from them. 5. A guage or apparatus for measuring the degree of exhaustion. 6. A screw for occasionally admitting the air when required.

The necessary requisites of a good air-pump are, 1. That it exhaust or rarify the air as much as possible. 2. That this be effected in the least possible time. 3. That there be a guage affixed to the pump, to ascertain with accuracy the degree of rarifaction. […]

To gain a clear idea of the action of the air-pump, it will be necessary to take it in pieces. You may now see that the barrel is made very cylindrical and smooth; the piston, which moves up and down, is made to fit it so exactly as to permit no air to pass between it and the barrel, and yet to move up and down with ease; the bottom of the piston when down lies as close as possible to the lower valve, in order to prevent any air remaining between them. You observe that in the piece screwed to the bottom of the piston, there is a hole, coinciding with one that goes through the piston; over this hole a small piece of oiled silk is tied, which is the piston valve; it opens upwards to give a passage to the air from below. In the brass plate on the bottom, you see another hole with a valve on the top; by this there is a passage for the air from any receiver placed on the plate of the pump to the cavity of the barrel at bottom; for the large plate of the pump is perforated with a hole, to meet the last mentioned one. These few parts are all that are essential to the pump, and will be sufficient to give you a very clear notion of the principles of those that are made in a complex form.

To work the pump, the piston is placed at the bottom of the barrel, and then lifted up; we suppose it to be so well fitted as to leave little or no air beneath; consequently; on lifting it up you raise the column of air that stands over the piston, and leave a cavity or space below in a great measure void of air, supposing that none could enter into this space through the valve in the plate of the pump. But as the air is very elastic, (as I shall prove to you hereafter) that which is in the receiver rushes through the lower valve into the void space in the barrel, till what is there, and in the receiver, become equally dense; by this means the quantity of air in the receiver is lessened, and as what remains still occupies the same space, it is said to be rarified or less dense.

This is one half of the operation; in the next place, the piston is to be carried down to the bottom of the barrel; by raising the piston I brought some of the air out of the barrel; by depressing the piston I shall get it out of the barrel also, and thus get rid of it quite; for by forcing the piston down, the air contained below it in the barrel (as it cannot return through the valves at the bottom of the plate,) is condensed by the piston, till it acquires elasticity enough to force open the valve in the piston, and make it’s [sic, throughout] escape into the common air, from whence it cannot return, being prevented by the valve. Thus a part of the air in the receiver is extracted, and by continuing the operation as much will be taken therefrom as may be required.

By means of the air-pump and it’s apparatus, you will soon become acquainted with the nature and properties of air. AIR is a fluid into which you are plunged the moment you are born, and without which you would in a moment be deprived of life. The nature of a fluid so important, should certainly engage the attention of every rational being; for no substance has a more universal influence on the general course of nature. The varieties in it’s temperature and weight are continually agitating our frame; to the action of these changes on our bodies we may attribute many of our sensations, both irksome and pleasant. Indeed we have always something to hope or fear from the vicissitudes of which it is susceptible. It contributes to the formation of hail, and sustains the clouds. Plants grow and are nourished by it. Without the air, there would be neither sound, nor voice, nor language, all fire would be extinct, animals would perish, and the whole world would languish and decay. It is almost impossible for you to think with indifference of the wonderful effects occasioned by this invisible agent. If your mind is capable of admiring these effects, it will not be insensible to the pleasure that is to be derived from a knowledge of their causes.

It is so pleasing to contemplate the first dawnings of improvement in science, and to see them rising gradually to perfection, through the successive labours of innumerable minds; that I cannot refrain from giving you short history of the air-pump.

The famous experiment of Torricellius, (to be explained in the next lecture) gave rise to the air-pump, and led the Florentine Academicians to contrive an instrument to procure a vacuum. For this purpose they filled a vessel with quicksilver, and then emptied it, taking care to prevent the air from entering while the quicksilver was going out: this instrument being very inconvenient, as well as imperfect, was soon laid aside.

Otto de Guericke, an ingenious magistrate of Hamburgh, invented the air-pump in 1654, and made the first public trial thereof about the same time at Ratisbon, before the Emperor of Germany, and several of the electors, who were highly delighted with the curious experiments exhibited by it. An account of these was soon after published by Scottus, a learned Jesuit. In 1672 Otto de Guericke gave an excellent narrative of his own experiments: the instrument was, however, still awkward and very imperfect. In order to try experiments with it, they were obliged to place their glasses, vessels, and other substances under water, to prevent the air from re-...