Robert Boyle

The teaching

Taught from his own books, above all The Sceptical Chymist, the Spring of the Air and The Christian Virtuoso.

The sceptical chymist

Boyle's teaching begins with a doubt about the furnace. In The Sceptical Chymist four friends talk in a garden: Themistius speaks for the four elements of the schools, Philoponus for the three principles of the chymists, salt, sulphur and mercury, Eleutherius listens, and Carneades, who speaks for Boyle, questions them both. He does not deny that bodies have parts. He denies that the fire shows what they are.

His reasons come from the laboratory. Fire does not only part bodies; it joins them too, as it makes glass from sand and ashes, so what comes out of the flask may be new bodies and not first ones. The same body gives different things in an open fire and in a closed vessel. Gold and some other bodies give no elements at all, whatever heat is used. And the salt, sulphur and mercury drawn from different bodies are not alike, so they are not simple. A chymist who calls whatever his fire leaves an element has named his products, not found the ingredients of nature.

What an element would be

Carneades then says what an element would have to be: certain first and simple bodies, wholly unmixed, made neither of other bodies nor of one another, which are the ingredients of every mixed body and into which every mixed body is finally resolved. Having set the definition, he doubts that any such bodies are found in all mixed bodies at all.

He tells of a willow raised by van Helmont in a tub of weighed earth and given nothing but water, which grew to a great weight while the earth lost almost none, and of a squash he raised himself in the same way. Water alone, it seemed, had become wood, bark and leaf. If one substance can take so many forms, Boyle reasons, the elements are not fixed kinds.

Matter and motion

In place of elements and principles he sets the corpuscles. There is one universal matter, common to all bodies, divided into very small particles of many sizes and shapes and set in motion. How the particles are joined, their texture, makes each body what it is, and all its qualities, colour, taste, heat and the power to dissolve or to heal, follow from size, shape, motion and arrangement. Matter and motion are his two great principles. A key, he says, is only iron of a certain shape, yet it has the power to open a lock because of its fit with another body; so the powers of things are their textures in relation to other textures, not hidden forms.

He shows it with saltpetre. Fire parts saltpetre into a volatile spirit and a fixed salt quite unlike it; join the two again and saltpetre comes back. Nothing was lost but an arrangement, and nothing was needed to restore it but the parts brought together. The world as a whole is for him like the great clock at Strasbourg, where every movement follows from the frame and the parts once the maker has set them going.

The spring of the air

Air, Boyle teaches, has weight and a spring: it is like a heap of tiny springs, or a fleece of wool, pressed down by the air above it and pushing back. With the pump he and Hooke built he draws the air out of a glass and watches what follows. A candle goes out and a coal stops glowing. The sound of a bell inside grows faint. Warm water begins to boil. The mercury of a barometer set inside falls as the air is drawn off and rises when it is let back in. Living creatures cannot last in the emptied glass, which shows that breath needs something in the air.

Then he measures the spring. He traps air in the short, closed leg of a bent glass tube and pours mercury into the long, open leg: double the pressure on the air and it takes half the room, treble it and it takes a third. The volume of a body of air varies inversely as the pressure on it.

Experiments plainly told

His method is as much his teaching as his results. A matter of fact is made by experiment, repeated and seen by witnesses, and then told so plainly and fully, with the vessels, the weights, the weather and the failures, that a reader could repeat it. He writes a whole essay on the unsuccessfulness of experiments, to warn that the same trial may fail with other materials or in other hands, and he holds that a failure honestly reported is worth more than a system built in haste. Judgement waits until the facts are many.

The search for the stone

The same man seeks the philosophers' stone all his life, and his corpuscles are his reason for hope. If every metal is made of one universal matter, differing only in the size, shape and texture of its particles, then nothing in nature forbids one metal from being changed into another: the task is to find the agent that can rearrange the parts. He prints an account of a mercury, purified by his own long labour, that grows hot when mixed with gold, and offers it as a possible step towards the stone. In another account he tells of a red powder that made gold worse, turning it into a baser metal: if a powder can make gold baser, he reasons, a powder may make a base metal better.

Quicksilver and its fumes are poisons, and nothing in these accounts is to be tried. Boyle himself kept his processes back, as the adepts of his day did.

The Christian virtuoso

Boyle teaches that the study of nature leads to God. The more closely the experimenter looks at the frame of the world, the eye, the order of the heavens, the fitting of every part to its use, the more he sees the wisdom of its maker, so that a virtuoso, a man given to experiment, is better placed than most to be a Christian. He warns against speaking of Nature as a goddess who abhors a vacuum or does nothing in vain: Nature is no agent at all, but the order God made and keeps. And he distinguishes what is above reason from what is against it, for some things of faith pass our understanding without contradicting it, as much in nature passes it too.

He left money in his will for sermons, preached every year, to defend the Christian religion against unbelievers without entering into the quarrels of Christians among themselves, so that the case of his books would go on being made after him.