194 Heilbron
calculation—directed interest and support to the study of natural philoso-
phy and mixed mathematics.
Another quantity that brought the natural philosopher close to the
people was the problem of counting them. The Swedish Academy of Sci-
ences organized the fi rst census in Europe in 1749. During the last third
of the eighteenth century, enlightened governments everywhere pursued
the number of its people; for wealth, according to mercantalist econom-
ics, was proportional to the size of the productive population. The rela-
tion between census data and natural knowledge may best be examined
in France, where the population refused to be counted lest revelation of
its prosperity raise its taxes. Numbering the king’s recalcitrant subjects
engaged the ablest natural philosophers and mixed mathematicians. Their
rhetoric is gratifying to the historian of exact science. “Experiment, re-
search, calculation are the probe of the sciences! What problems could
not be so treated in administration! What sublime questions could not be
submitted to the law of calculation!” Men of such science had only to read
the “thermometer of public prosperity,” “the barometer [of the nation],”
that is, the number of citizens, to know the health of the state. The Paris
Academy opened its pages to vital statistics; but the peasantry refused to
allow itself to be counted even in so prestigious a place. The calculators
had fi nally to invent sampling methods. Laplace worked out the effect of
the size of the sample on the probable error of the estimated population.
Full data from cooperating parishes combined with partial information
from the rest then gave a number that might or might not have been the
population of France.^53- Physics for Love
By doing physics for love Deluc did not mean without hope of reputa-
tion or emolument. The two examples he offers, himself and Lichtenberg,
stood high in the Republic of Letters and supported themselves by their
knowledge of natural philosophy. After leaving his native Geneva in 1773
when his business failed, Deluc came into the grand sinecure of reader in
natural philosophy to Queen Charlotte of England, who housed him in
Windsor Castle with an income that met his needs. Lichtenberg was a pro-
fessor and privy councilor. Both were members of the Royal Society and
other prestigious academies. Their love for physics was the philosopher’s
devotion to seeking and saying the truth. In 1798, when Deluc enrolled
Lichtenberg along with himself among the few lovers left in the world of
physics, he had in mind as counterexamples the wanton mindless natural
philosophers of Germany who had taken up with French chemistry. This