d gaseous constitution, to deduce minimum
values for the temperatures prevailing in the area of their development.
These came out 27,700 deg. C. for the strata lying immediately above, and
68,400 deg. C. for the strata lying immediately below the photosphere, the
former being regarded as the region _into_ which, and the latter as the
region _from_ which the eruptions took place. In this calculation, no
prominences exceeding 40,000 miles (1.5') in height were included. But
in 1884, G. A. Hirn of Colmar, having regard to the enormous velocities
of projection observed in the interim, fixed two million degrees
Centigrade as the lowest _internal_ temperature by which they could be
accounted for; although admitting the photospheric condensations to be
incompatible with a higher _external_ temperature than 50,000 deg. to
100,000 deg. C.[723]

This method of going straight to the sun itself, observing what goes on
there, and inferring conditions, has much to recommend it; but its
profitable use demands knowledge we are still very far from possessing.
We are quite ignorant, for instance, of the actual circumstances
attending the birth of the solar flames. The assumption that they are
nothing but phenomena of elasticity is a purely gratuitous one.
Spectroscopic indications, again, give hope of eventually affording a
fixed point of comparison with terrestrial heat sources; but their
interpretation is still beset with uncertainties; nor can, indeed, the
expression of transcendental temperatures in degrees of impossible
thermometers be, at the best, other than a futile attempt to convey
notions respecting a state of things altogether outside the range of our
experience.

A more tangible, as well as a less disputable proof of solar radiative
intensity than any mere estimates of temperature, was provided in some
experiments made by Professor Langley in 1878.[724] Using means of
unquestioned validity, he found the sun's disc to radiate 87 times as
much heat, and 5,300 times as much light as an equal area of metal in a
Bessemer converter after the air-blast had continued about twenty
minutes. The brilliancy of the incandescent steel, nevertheless, was so
blinding, that melted iron, flowing in a dazzling white-hot stream into
the crucible, showed "deep brown by comparison, presenting a contrast
like that of dark coffee poured into a white cup." Its temperature was
estimated (not quite securely)[725] at about 2,000 deg. C.; and no
allow