The fluctuation in the sun’s direct heating power amounts to 1/15th,
which is too considerable a fraction of the whole intensity not
to aggravate in a serious degree the sufferings of those who are
exposed to it in thirsty deserts without shelter. The amount of these
sufferings, in the interior of Australia for instance, are of the
most frightful kind, and would seem far to exceed what have ever been
undergone by travellers in the northern deserts of Africa. Thus
Captain Sturt, in his account of his Australian exploration, says:
“The ground was almost a molten surface; and if a match accidentally
fell upon it, it immediately ignited.” Sir John Herschel has observed
the temperature of the surface soil in South Africa as high as 159°
Fahrenheit. An ordinary lucifer-match does not ignite when simply
pressed upon a smooth surface at 212°; but _in the act of withdrawing
it_ it takes fire, and the slightest friction upon such a surface of
course ignites it.