Various experiments have lead to the general conclusion that the
power of absorption is always in the same proportion as the power of
radiation. It must be so. Were any substance a powerful radiator and at
the same time a bad absorber, it would necessarily radiate faster than
it would absorb, and its reduction of temperature would continue without
limit. It has, furthermore, been proved that the absorptive property of
substances increases as their reflecting qualities diminish. Hence, the
radiating power of a surface is inversely as its reflecting power. It is
for this reason that the polished metallic sheathing on the cylinders
of locomotive engines, and on the boilers of steam fire engines, is
not only ornamental but essentially useful. Decisive tests have also
established the fact that radiation is effected more or less by color.
"A black porcelain tea pot," observes Dr. Lardner, "is the worst
conceivable material for that vessel, for both its material and color
are good radiators of heat, and the liquid contained in it cools with
the greatest possible rapidity; a polished silver or brass tea urn is
much better adapted to retain the heat of the water than one of a dull
brown, such as is most commonly used."

A few facts like those above stated afford more decisive information
regarding the nature of heat than columns of theory or speculation. Yet
it is rather strange that when so many learned and reliable men have,
experimented so much and commented with such persuasiveness upon the
subtile agency of heat and the vast amount of waste that must accrue by
injudicious management, comparatively few have availed themselves of the
united labors of these indefatigable pyrologists; manufacturing owners
and corporations still persisting in having their steam boilers painted
black or dull red and leaving them exposed to the atmosphere. Some
persons, who pass themselves off very satisfactorily as clever