Descartes: A Biography

c CUNYB/Clarke     December, :

Once More into Battle 

In order for us to know also if variations in the weather and place do not affect the

[height of the] mercury, I am sending you a strip of paper two and a half feet long,

onwhich the third and fourth inches above the two-foot mark are divided into lines. I

shall keep an exactly similar one here, to see if our observations agree. I am asking you,

then, to observe the point to which the mercury rises on this scale when the weather

is warm and when it is cold, and when the wind blows from the north and from the

south. In order to let you know that there will be variations, and to persuade you to

report your observations to me very honestly, I will tell you that, on Monday last,

the height of the mercury was exactly two feet three inches on this scale. Yesterday,

which was Thursday, it was a little above two feet four inches. Today, however, it

has dropped again by three or four lines. I have a tube that remains attached to the

same place day and night, in order to make these observations. However, I think it

would be best not to tell anyone about them yet, and to wait until Mr. Pascal’s book is

published. (v.–)

Since Descartes was equally confident that the apparent vacuum in these

glass tubes was some kind of body, he asked Mersenne to conduct another

experiment by setting fire to a piece of sulphur – which could be set alight

byusing a mirror or lens – suspended by a string in the ‘vacuum’. He

needed Mersenne’s help because the Sun was not strong enough, at least

not in December, to do that kind of experiment in Egmond.

Descartes’ observations contrast markedly with those reported even-

tually by Florin and Pascal, that there was no change in the height of

the mercury despite fluctuating weather conditions on the Puy-de-Dome.ˆ

Descartes did not publish his results, and almost two years later (after

Mersenne had died) he was still inquiring about the results of the Puy-

de-Dˆome experiment.When he was told about those results, in July

,hewas delighted to hear the news. He claimed that the results were

entirely consistent with his principles, and even that he had suggested

the experiment to Pascal, who otherwise would never have attempted it,

since he had expected the opposite result. Since Pascal had promised to

refute the Cartesian subtle matter in his first publication,New Experiments

concerning the Vacuum, Descartes asked Carcavi to tell Pascal, if he met him

in Paris, that he was still waiting for the promised refutation.This request

remained unanswered. By the time Carcavi looked for Pascal to pass on

the request, Pascal and his whole family had left Paris to live with his sister

and brother-in-law in Clermont, and Descartes had left Egmond to visit

Stockholm. Pascal did not return to Paris until after Descartes’ death.

This unresolved debate about the metaphysical status of the apparently

empty space at the top of a Torricelli tube, between Descartes and No ̈el