reduced by
modern scientific discoveries respecting these bodies, yet in other
respects the very confidence engendered by the exactness of modern
astronomical computations has proved a source of terror. There is
nothing more remarkable, for instance, in the whole history of cometary
superstition, than the panic which spread over France in the year 1773,
in consequence of a rumour that the mathematician Lalande had predicted
the occurrence of a collision between a comet and the earth, and that
disastrous effects would inevitably follow. The foundation of the rumour
was slight enough in all conscience. It had simply been announced that
Lalande would read before the Academy of Sciences a paper entitled
'Reflections on those Comets which can approach the Earth.' That was
absolutely all; yet, from that one fact, not only were vague rumours of
approaching cometic troubles spread abroad, but the statement was
definitely made that on May 20 or 21, 1773, 'a comet would encounter the
earth.'[43] So great was the fear thus excited, that, in order to calm
it, Lalande inserted in the 'Gazette de France' of May 7, 1773, the
following advertisement:--'M. Lalande had not time to read his memoir
upon comets which may approach the earth and cause changes in her
motions; but he would observe that it is impossible to assign the epochs
of such events. The next comet whose return is expected is the one which
should return in eighteen years; but it is not one of those which can
hurt the earth.'

This note had not the slightest effect in restoring peace to the minds
of unscientific Frenchmen. M. Lalande's study was crowded with anxious
persons who came to inquire about his memoir. Certain devout folk, 'as
ignorant as they were imbecile,' says a contemporary journal, begged the
Archbishop of Paris to appoint forty hours' prayer to avert the danger
and prevent the terrible deluge. For this was the particular form most
men agreed that the danger would take. That prelate was on the point,
indeed, of complying with their request, and would have done so, but
that some members of the Academy explained to him that by so doing he
would excite ridicule.

Far more effective, and, to say truth, far better judged, was the irony
of Voltaire, in his deservedly celebrated 'Letter on the Pretended
Comet.' It ran as follows:--

'Grenoble, May 17, 1773.

'Certain Parisians who are not philosophers, and who, if we are to
believe them, will not have time to