Nothing has been added but movement. There is no caloric
substance. Heat is a mode of motion. The particles of iron have been
made to vibrate among themselves. When the rapidity of movement
reaches four hundred and sixty millions of millions of vibrations per
second it so affects the eye that we say it is red-hot. When other
systems of vibration have been added for yellow, etc., up to seven
hundred and thirty millions of millions for the violet, and all
continue in full play, the eye perceives what we call white heat. It
is a simple illustration of the readiness of seeming solids to vibrate
with almost infinite swiftness.
I have been to-day in what is to me a kind of heaven below--the
workshop of my much-loved friend, John A. Brashear, in Allegheny, Pa.
He easily makes and measures things to one four-hundred-thousandth of
an inch of accuracy. I put my hand for a few seconds on a great piece
of glass three inches thick. The human heat raised a lump detectable
by his measurements. We were testing a piece of glass half an inch
thick; and five inches in diameter. I put my two thumbnails at the two
sides as it rested on its bed, and could see at once that I had
compressed the glass to a shorter diameter. We twisted it in so many
ways that I said, "That is a piece of glass putty." And yet it was the
firmest texture possible to secure.
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