SIR WILLIAM PETTY AND POLITICAL ARITHMETIC 83

made no bones about admitting when he wanted to get some-
thing done. An impartial contemporary comparing the Politicall
Arithmitick with the Sceptical Chymist might have been at pains
to forecast whether the progress of chemistry would justify the
comparison which Jeremy Bentham made a century later. Refer-
ring to Lavoisier's discoveries and the state of social enquiries
Bentham exclaisjis, "Think of what chemistry was before that
time—think of what it has since become!"

The training of an English economist makes no provision for
studying the "history of trades, receipts and experiments, phar-
macy and jewelling." So it will not be profitless to pursue Ben-
tham's counsel. Between the work of Boyle and that of Lavoisier
the course of chemistry did not run smooth. The reason why the
Sceptical Chymist signalizes the dichotomy between modern
chemistry and alchemy is that the air pump of "the immortal
Mr. Boyle" had proved beyond dispute the existence of the third
state of matter. Aristotle's self-evident doctrine that air is weight-
less had been conclusively disproved. The spirits of the retort
were for the first time recognized as matter in an attenuated form,
compressible—as Boyle had shown—according to ascertainable
laws. The new laws of gas mechanics were established by the
ungendemanly process of manual experimentation without assis-
tance from the original definitions of the subject. After nineteen
centuries of Aristotelian futilities the common pump had come
into its own. The doctrines which Aristotle had exercised the full
powers of his ingenuity to discredit had been spread abroad by
Gassendi's commentaries on Epicurus. Hooke's experiments on
gunpowder and Mayow's work on breathing had set the stage
for a correct understanding of combustion and oxidation. It
seemed as if the world of science was ready for the recognition
that matter, contrary to self-evident principles, is not continuous.

Seemingly every obstacle to useful knowledge about the most
ancient of chemical industries had been removed. It was now
known that metals gain weight when heated in air to form a calx
(metallic oxide). A straightforward explanation of this fact is that
they combine like charcoal or sulphur with Hooke's nitro-aerial