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theory of matter, which is essential for understanding why gas pressure might increase with decreased volume: the particles are simply pushed closer together, beyond their 'natural' mutual distances and consequently into increased collisions with each other.

When he published the law linking volume and pressure, Boyle himself referred to it as Richard Towneley's hypothesis. In 1661, Towneley and his friend Henry Power had used a barometer to measure air pressure at different altitudes, and thereby deduced a relationship between air pressure and air density. The resulting book, "Experimental Philosophy", was not published until 1663, but Towneley had discussed the experiments with Boyle and also shown him an early draft of the book. Boyle tested this hypothesis within a closed chamber apparatus which made use of vacuum pumps, publishing the results in 1662: and thus the resulting law bears his name.

The apparatus itself was built by his assistant Robert Hooke, who is also held to have been a better mathematician than Boyle, and who thus might well have done the lion's share of the data crunching. Hooke later developed what is still known as Hooke's law of elasticity, which he summarised as "Ut tension, sic vis", as the extension, so the force. Clearly the two lines of reasoning are tightly interrelated.

Boyle's law is sometimes known as the Boyle-Mariotte law, to acknowledge the 1676 contributions of the French physicist Edme Mariotte. There is some question as to whether Mariotte did in fact discover the principle independently of Boyle's writings.

It is important to appreciate that Boyle's law is a real-world approximation best suited for anticipating the effects of relatively small change on a closed system, rather than an absolute holding true across all possible pressures at all possible temperatures. At greater pressures or higher temperatures, the assumed simple collision and bounce-back begins to be replaced by a model where some molecules continue to be mutually repelled, while others begin to interact chemically with each other as their activation energy is exceeded. Similarly, at higher complexities of molecules, the clean assumption of simple collision theory, that molecules approximate a spherical shape equally able to react in all directions, breaks down.

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