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
space, across which heat must pass by radiation. It is by radiation
ultimately, therefore, that all bodies get heated. This being so, it is
well to increase the radiating power of flame as much as possible. Now,
radiating power depends on two things: the presence of solid matter in the
flame in a fine state of subdivision, and the temperature to which it is
heated. Solid matter is most easily provided by burning a gas rich in dense
hydrocarbons, not a poor and non-luminous gas. To mix the gas with air so
as to destroy and burn up these hydrocarbons seems therefore to be a
retrograde step, useful undoubtedly in certain cases, as in the Bunsen
flame of the laboratory, but not the ideal method of combustion. The ideal
method looks to the use of a very rich gas, and the burning of it with a
maximum of luminosity. The hot products of combustion must give up their
heat by contact. It is for them that cross tubes in boilers are useful.
They have no combustion to be interfered with by cold contacts. The _flame_
only should be free.

The second condition of radiation was high temperature. What limits the
temperature of a flame? Dissociation or splitting up of a compound by heat.
So soon as the temperature reac