ge suspended on
springs. By observing the degree of heat obtained by different kinds
of motion we may form an estimate of the quantity of exercise given by
each. Thus, for example, if you turn out to walk in winter with cold
feet, in an hour's time you will be in a glow all over; ride on
horseback, the same effect will scarcely be perceived by four hours'
round trotting; but if you loll in a carriage, such as you have
mentioned, you may travel all day, and gladly enter the last inn to
warm your feet by a fire. Flatter yourself then no longer that half an
hour's airing in your carriage deserves the name of exercise.
Providence has appointed few to roll in carriages, while he has given
to all a pair of legs, which are machines infinitely more commodious
and serviceable. Be grateful, then, and make a proper use of yours.
Would you know how they forward the circulation of your fluids, in the
very action of transporting you from place to place; observe when you
walk that all your weight is alternately thrown from one leg to the
other; this occasions a great pressure on the vessels of the foot, and
repels their contents; when relieved, by the weight being thrown on
the other foot, the vessels of the first are allowed to replenish,
and, by a return of this weight, this repulsion again succeeds, thus
accelerating the circulation of the blood. The heat produced in any
given time depends on the degree of this acceleration; the fluids are
shaken, the humors attenuated, the secretions facilitated, and all
goes well; the cheeks are ruddy, and health is established. Behold
your fair friend at Auteuil;[24] a lady who received from bounteous
nature more really useful science than half a dozen of such pretenders
to philosophy as you have been able to extract from all your books.
When she honors you with a visit, it is on foot. She walks all hours
of the day, and leaves indolence, and its concomitant maladies, to be
endured by her horses. In this see at once the preservative of her
health and personal charms. But when you go to Auteuil, you must have
your carriage, tho it is no farther from Passy to Auteuil than from
Auteuil to Passy.

[Footnote 24: The reference is to Madame Helvetius, whom Franklin knew
as the widow of the writer Claude Adrien Helvetius. Her home was long
a center of literary society in France. The friendship with Franklin
was a notable incident in his career as American Ambassador to France.
See his letter to her pri