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Robert Boyle (1627-1691)

Robert Boyle was born at Lismore Castle, Munster on 25 January 1627, the fourteenth child and seventh son of Richard Boyle, 1st Earl of Cork. Robert Boyle was educated mainly by tutors and himself. He had no formal university education but read widely and made contact with many of the most important natural philosophers of his day, both at home and abroad.

He had independent means which enabled him to have his own laboratory and to support religious charities. He was active in the ‘Invisible College’, an informal body devoted to the ‘new philosophy’ which in 1663 became the Royal Society, of which he was a Council member. He moved to Oxford in 1654, where he set up a laboratory with Robert Hooke as his assistant There he did most of his experimental work until 1668 when he went to live in London with his sister Lady Ranelagh. (reference 90) He indeed developed a keen interest in the work of artisans because they tend to know more than anyone else about the materials of their trades. He makes a general remark about religious beliefs that ‘though we cannot always give a reason for what we believe, we should ever be able to give a reason why we believe it’, which is surely a precept that guided his attitude to natural philosophy as well.

Boyle was a prolific writer and experimenter on most scientific subjects that were attracting interest at the time. He investigated some alchemical claims about which he was largely skeptical in his published works. He was a devoutly religious man but wrote mainly about practical and ethical religious matters rather than engaging in theological controversy. He argued for the tolerance of different religious beliefs, and spent a good deal of money on propagating the gospel in New England and the Orient, sponsoring translations of the Bible into foreign languages.

See: The Mechanical Origine or Production of Corrosiveness and Corrosibility

He published many experimental reports and did original work on chemical indicators, human blood, color, fire, medicine, and hydrostatics. With Hooke he developed Guericke’s air pump, which he needed for his experiments. His first major publication was his book on the ‘spring’ of the air (1660), in the second edition of which (1662) we find the first statement of what came to be known as ‘Boyle’s Law’, about the relation between the pressure and volume of gases.

Perhaps Boyle’s most interesting and influential contribution was his ‘corpuscular or mechanical hypothesis’, probably the fullest and most detailed development of physical atomism up to his time. His work on this begins in earnest in The Sceptical Chymist (1661) but it receives its clearest exposition in The Origin of Forms and Qualities (1666), and he returns to it in many of his later works. A useful summary of its basic principles is to be found in his About the Excellency and Grounds of the Mechanical Philosophy (1674).

Boyle leads up to his hypothesis by considering in detail and attacking the forms of explanation and their basic concepts that he found natural philosophers using in the sixteenth and early seventeenth centuries. They fall into two main classes which sometimes overlap: those favored by the ‘chymists’ or ‘spagyrists’, and those favored by the ‘Aristotelians’ or ‘peripatetics’. The chymists’ explanations were based on the tria prima, the three chemical ‘principles’ salt, sulfur, and mercury which they regarded as ingredients of all substances. These explanations depended on the presence in observable bodies and materials of various proportions of the principles. They were not identical with the chemical substances of the same names but were kinds of essences of them.

Observable objects, according to the hypothesis, are composed of innumerable solid corpuscles separated by empty space which allows the physical divisibility of the objects, their expansion and contraction, and changes of shape. Chemical reactions may be explained by changes of texture involving the inter-penetration of groups of corpuscles and the entrapment or release of individual corpuscles by groups of them.

The hypothesis is highly versatile just because the corpuscles are composed of one universal matter and so have few qualities.The test of the worth of the hypothesis will be empirical and will depend upon the comparison of its deduced consequences in specific circumstances with the results of experiment; that is, on the adequacy of its explanations and the success of its predictions. If the hypothesis is contradicted by observed evidence, it may be modified or rejected.

Its greatest challenges have been regarded as the explanation of such properties as gravitational, magnetism and electrical ones. These were widely regarded as ‘occult’ and many natural philosophers of the time, including Boyle, hoped to avoid the use of occult qualities and entities, and to show that they could be given mechanical explanations. For Boyle something was occult if it was unobservable and postulated on the sole ground that it would explain a particular property or phenomenon and there was no description of it except in terms of what it was intended to explain.

Boyle hoped that gravitational, magnetic, and electrical properties, although provisionally acceptable in what he called ‘intermediate’ explanations, would be given more fundamental explanations in terms of the mechanical qualities of the corpuscles. Intermediate explanations might help the layman to deal with some phenomena but they would not satisfy the corpuscularian natural philosopher. It is safe to say that no remotely plausible explanation that would satisfy him was forthcoming for these phenomena.

Boyle’s experimental reports are sometimes criticized for being unsystematic and trivial, and for not contributing to the support of his hypothesis. However, in assessing his work it is important to realize how primitive natural philosophy was at that time compared with physical science as we now know it. Bacon had stressed the need, before explanation could begin, for a usable collection of clear descriptions of even everyday phenomena based on careful observation. Philosophers were far readier to speculate about the description of natural events rather than to join the ‘sooty empirics’ in close observation of them. Boyle took Bacon’s admonition seriously and as a result many of his experiments were not intended to provide support for his hypothesis but merely descriptions of the facts to be explained.

Many more were intended to investigate simple phenomena that would merely provide prima facie evidence for the plausibility of corpuscular explanations. His experiments on the color-changes when such materials as horn and glass were scraped strongly suggested that changes in superficial corpuscular structures were responsible. Finally, Boyle stresses the enormous amount of experimental work that will be needed to develop and test detailed explanations of complex phenomena such as chemical interactions. He had to spend a great deal of time in designing and constructing suitable apparatus. He never claimed to have got very far in providing firm empirical evidence for complex corpuscular explanations but he remained optimistic.

It has recently been argued, partly on the basis of Boyle’s unpublished notes, that his interest in alchemy has been greatly underestimated by earlier scholars. It is well known that he attempted to confirm many of the alchemists’ experimental claims but he is also said to have believed in the existence of the Philosopher’s Stone and to have accepted some alchemical explanations. It has even been suggested, rather obscurely, that he saw alchemy as connecting the material world with the spiritual world.

In his published work he clearly accepts the possibility of the transmutation of metals but that is because a corpuscular explanation would be readily available. He respects the alchemists’ experimental work because he strongly approves of the experimental investigation of the natural world and he thinks that the ‘nobler’ of the alchemists have made important empirical discoveries. His published comments on their theories, their search for the Philosopher’s Stone, and their penchant for secrecy are usually critical.