Monday, May 26, 2008

Wooly metaphors in seventeenth century science

I have a 2000 word essay to write about Descartes, which is one reason I haven't written anything here recently.

While researching it, I discovered that Pascal carried out experiments on a variety of things, including wine and wool. That led me into checking up about wool and experiments in the seventeenth century, and it seemed that wool - by which they meant fleece - was a useful metaphor for air. They were investigating about air pressure. We are used to thinking about air as having weight, but in the seventeenth century this was a matter of debate.

Torricelli compared a column of air to a cylinder filled by wool. When a weight is placed on the top, the wool is compressed. He said that if a knife was thrust through the cylinder, the wool-pressure is unchanged. Pascal pointed out that the weight of the wool itself compresses the wool at the bottom of the heap.

Boyle used the analogy in a different way, referring to wool that was being compressed. He states "upon the removal of the external pressure, by opening the hand more or less, the compressed wool doth, as it were, spontaneously expand ... till the fleece hath either regained its former dimensions", or at least as close to its dimensions as the "compressing hand... will permit".

Descartes too used a wooly analogy, but unfortunately his was wrong. Asked why mecury did not flow out of an inverted tube, he said that the air was like wool and "the ether in its pores to be like whirlwinds moving about in the wool." Everything was moving in a circle: there couldn't be a vacuum at the top, because Descartes thought vacuums were impossible.

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