andescence by the heat of the flame. The heat is due to the clashing
of the particles, the light is due to the heated solid matter in the
flame. Let me see if I can show you that. I am setting free in this
bottle some hydrogen, which I am about to ignite at the end of this
piece of glass tube (Fig. 38 A). I shall be a little cautious, because
there is danger if my hydrogen gets mixed with air. There is my hydrogen
burning; but see, it gives little or no light. But this candle flame
gives light. Why? The light of the candle is due to the intensely heated
solid matter in the flame; the absence of light in the hydrogen flame
depends on the absence of solid matter. Let me hold clean white plates
over both these flames. See the quantity of black solid matter that I am
able to collect from this candle flame (Fig. 38 B). But my hydrogen
yields me no soot or solid matter whatsoever (Fig. 38 A). The plate
remains perfectly clean, and only a little moisture collects upon it.
The light that candle gives depends upon the solid matter in the flame
becoming intensely heated. If what I say be true, it follows that if I
take a flame which gives no light, like this hydrogen flame (Fig. 39 A),
and give it solid particles, I ought to change the non-luminous flame
into a luminous one. Let us see whether this be so or not. I have here a
glass tube containing a little cotton wadding (Fig. 39 B _a_), and I am
about to pour on the wadding a little ether, and to make the hydrogen
gas pass through the cotton wadding soaked with ether before I fire it.
And now if what I have said is correct, the hydrogen flame to which I
have imparted a large quantity of solid matter ought to produce a good
light, and so it does! See, I have converted the flame which gave no
light (Fig. 39 A) into a flame which gives an excellent light merely by
incorporating solid matter with the flame (Fig. 39 B). What is more, the
amount of light that a flame gives depends upon the amount or rather the
number of solid particles that it contains. The more solid particles
there are in the flame, the greater is the light. Let me give you an
illustration of this. Here is an interesting little piece of apparatus
given to my predecessor in the chair of chemistry at the London Hospital
by the Augustus Harris of that day. It is one of the torches formerly
used by the pantomime fairies as they descended from the realms of the
carpenters. I have an alcohol flame at the top of the torch whi