The most remarkable and, at first sight, astounding thing about this
furnace is, however, that it works solely by radiation. The flames do not
touch the material to be heated; they burn above it, and radiate their heat
down to it. This I regard as one of the most important discoveries in the
whole subject, viz., that to get the highest temperature and greatest
economy out of the combustion of coal, one must work directly by radiant
heat only, all other heat being utilized indirectly to warm the air and gas
supply, and thus to raise the flame to an intensely high temperature.

It is easy to show the effect of supplying a common gas flame with warm air
by holding it over a cylinder packed with wire gauze which has been made
red hot. A common burner held over such a hot air shaft burns far more
brightly and whitely. There is no question but that this is the plan to get
good illumination out of gas combustion; and many regenerative burners are
now in the market, all depending on this principle, and utilizing the waste
heat to make a high temperature flame. But although it is evidently the
right way to get light, it was by no means evidently the right way to get
heat. Yet so it turns out, not by warming solid objects or by dull warm
surfaces, but by the brilliant radiation of the hottest flame that can be
procured, will rooms be warmed in the future. And if one wants to boil a
kettle, it will be done, not by putting it into a non-luminous flame, and
so interfering with the combustion, but by holding it near to a freely
burning regenerated flame, and using the radiation only. Making toast is
the symbol of all the heating of the future, provided we regard Mr.
Siemens' view as well established.

The ideas are founded on something like the following considerations: Flame
cannot touch a cold surface, i.e., one below the temperature of combustion,
because by the contact it would be put out. Hence, between a flame and the
surface to be heated by it there always intervenes a comparatively cool