Descartes: A Biography

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 Descartes: A Biography

sickness.However, Beeckman was only forty-three years old at that

stage, and he was to live for another six years. Descartes also seems to

have been ill himself during the summer of. Although he returned to

Amsterdam from Dordrecht in good health, Beeckman writes in October

about his convalescing from a rather serious but unspecified illness.This,

together with the voyage to Denmark, may explain why Descartes writes

to Mersenne, in October or November, that he had done almost no

work on his project ‘for three or four months’ (i.).

With a return to work onThe World, Descartes takes up again some of

the familiar scientific questions that had distracted him during the previous

two years. He had discussed an explanation of the mercury barometer in

June (i.), and he now plans to discuss gravity in what he invariably

calls ‘my treatise’ (i.). He advises Ville-Bressieux that they are agreed

about some basic principles; for example, that ‘there is only one material

substance which receives from some external agent the action or means

of moving itself locally’ (i.). The question about falling bodies, in a

vacuum or in air, is still unresolved, although Descartes is quick to mention

that he does not think there is any such thing as a vacuum (i.).

Descartes’ friend Reneri, who had been appointed a tutor to children in

Leiden, was appointed to a chair of philosophy at Deventer onOctober

. Descartes commented that the new appointment was ‘in an academy

that was not very famous; however, the professors are better paid and live

more comfortably than at Leiden or Franeker, where Mr Reneri could

have been appointed earlier if he had not refused or neglected it’ (i.–

). This was probably the reason why, in May, Descartes moved once

again, this time to Deventer.

Before departing, however, Descartes addressed one of the most

intractable problems from ancient geometry, the so-called Pappus prob-

lem. Jacob van Gool (usually known as Golius), whom Descartes had met

during his short stay at Leiden, had sent this problem simultaneously to

anumber of people.Descartes’ proposed solution to the problem was

subsequently published in theGeometry(), but it was evidently for-

mulated during the winter of–, since he told Mersenne in April

that he had worked on it for ‘five or six weeks’ (i.). He was

thus able to send his solution to Golius in January,atthe same time

promising to send him the early part of theDioptricsin which he had

worked out the sine law of refraction.Once that rather major mathe-

matical puzzle was solved, he returned to his principal work,The World.