is adverse and irreversible.

After every deduction, however, has been made, we still find that
several ideas of permanent value were embodied in this comprehensive
sketch of the solar constitution. The principal of these were; first,
that the sun is a mainly gaseous body; secondly, that its stores of heat
are rendered available at the surface by means of vertical
convection-currents--by the bodily transport, that is to say, of
intensely hot matter upward, and of comparatively cool matter downward;
thirdly, that the photosphere is a surface of condensation, forming the
limit set by the cold of space to this circulating process, and that a
similar formation must attend, at a certain stage, the cooling of every
cosmical body.

To Warren de la Rue belongs the honour of having obtained the earliest
results of substantial value in celestial photography. What had been
done previously was interesting in the way of promise, but much could
not be claimed for it as actual performance. Some "pioneering
experiments" were made by Dr. J. W. Draper of New York in 1840,
resulting in the production of a few "moon-pictures" one inch in
diameter;[446] but slight encouragement was derived from them, either to
himself or others. Bond of Cambridge (U.S.), however, secured in 1850
with the Harvard 15-inch refractor that daguerreotype of the moon with
which the career of extra-terrestrial photography may be said to have
formally opened. It was shown in London at the Great Exhibition of 1851,
and determined the direction of De la Rue's efforts. Yet it did little
more than prove the art to be a possible one.

Warren de la Rue was born in Guernsey in 1815, and died in London April
19, 1889. Educated at the Ecole Sainte-Barbe in Paris, he made a large
fortune as a paper manufacturer in England, and thus amply and early
provided the material supplies for his scientific campaign. Towards the
end of 1853 he took some successful lunar photographs. They were
remarkable as the first examples of the application to astronomical
light-painting of the collodion process, invented by Archer in 1851; and
also of the use of reflectors (De la Rue's was one of thirteen inches,
constructed by himself) for that kind of work. The absence of a driving
apparatus was, however, very sensibly felt; the difficulty of moving the
instrument by hand so as accurately to follow the moon's apparent motion
being such as to cause the discontinuance of the experiments until 18