e else even came abreast
their line of thought, let alone passing it.

But then, in 1824, a French philosopher, Sadi Carnot, caught step with
the great Englishmen, and took a long leap ahead by explicitly stating
his belief that a definite quantity of work could be transformed into
a definite quantity of heat, no more, no less. Carnot did not, indeed,
reach the clear view of his predecessors as to the nature of heat, for
he still thought it a form of "imponderable" fluid; but he reasoned none
the less clearly as to its mutual convertibility with mechanical work.
But important as his conclusions seem now that we look back upon
them with clearer vision, they made no impression whatever upon his
contemporaries. Carnot's work in this line was an isolated phenomenon
of historical interest, but it did not enter into the scheme of the
completed narrative in any such way as did the work of Rumford and Davy.

The man who really took up the broken thread where Rumford and Davy had
dropped it, and wove it into a completed texture, came upon the scene
in 1840. His home was in Manchester, England; his occupation that of
a manufacturer. He was a friend and pupil of the great Dr. Dalton.
His name was James Prescott Joule. When posterity has done its final
juggling with the names of the nineteenth century, it is not unlikely
that the name of this Manchester philosopher will be a household word,
like the names of Aristotle, Copernicus, and Newton.

For Joule's work it was, done in the fifth decade of the century, which
demonstrated beyond all cavil that there is a precise and absolute
equivalence between mechanical work and heat; that whatever the form of
manifestation of molar motion, it can generate a definite and measurable
amount of heat, and no more. Joule found, for example, that at the
sea-level in Manchester a pound weight falling through seven hundred and
seventy-two feet could generate enough heat to raise the temperature
of a pound of water one degree Fahrenheit. There was nothing haphazard,
nothing accidental, about this; it bore the stamp of unalterable law.
And Joule himself saw, what others in time were made to see, that this
truth is merely a particular case within a more general law. If
heat cannot be in any sense created, but only made manifest as a
transformation of another kind of motion, then must not the same
thing be true of all those other forms of "force"--light, electricity,
magnetism--which had been shown to