Neither is the composition of the Black Smoke known, which the
Martians used with such deadly effect, and the generator of the
Heat-Rays remains a puzzle.  The terrible disasters at the Ealing
and South Kensington laboratories have disinclined analysts for further
investigations upon the latter.  Spectrum analysis of the black powder
points unmistakably to the presence of an unknown element with a
brilliant group of three lines in the green, and it is possible that
it combines with argon to form a compound which acts at once with
deadly effect upon some constituent in the blood.  But such unproven
speculations will scarcely be of interest to the general reader, to
whom this story is addressed.  None of the brown scum that drifted
down the Thames after the destruction of Shepperton was examined at
the time, and now none is forthcoming.