object seems to glow with a dull red light; becoming hotter, the
vibrations increase in rapidity. When they reach 765,000,000,000,000
per second the color becomes violet, and the eye can observe them no
farther. Between these numbers are those of different rapidities,
which affect the eye--as orange, yellow, green, blue, indigo, in an
almost infinite number of shades--according to the sensitiveness
of the eye.

We now see how our dark immensity of attractive atoms can become
luminous. A force of compression results in vibrations within,
communicated to the ether, discerned by the eye. Illustrations are
numerous. If we suddenly push a piston into a cylinder of brass,
the force produces heat enough to set fire to an inflammable substance
within. Strike a half-inch cube of iron a moderate blow and it becomes
warm; a sufficient blow, and its vibrations become quick enough to
be seen--it is red-hot. Attach a thermometer to an extended [Page
19] arm of a whirling wheel; drive it against the air five hundred
feet per second, the mercury rises 16°. The earth goes 98,000 feet
per second, or one thousand miles a minute. If it come to an
aerolite or mass of metallic rock, or even a cloudlet of gas,
standing still in space, its contact with our air evolves 600,000°
of heat. And when the meteor comes toward the world twenty-six miles
a second, the heat would become proportionally greater if the meteor
could abide it, and not be consumed in fervent heat. It vanishes
almost as soon as seen. If there were meteoric masses enough lying
in our path, our sky would blaze with myriads of flashes of light.
Enough have been seen to enable a person to read by them at night.
If a sufficient number were present, we should miss their individual
flashes as they blend their separate fires in one sea of
insufferable glory. The sun is 1,300,000 times as large as our