Gomel, _Les Causes financieres de la Revolution_ (Paris,
1893); R. Stourm, _Les Finances de l'ancien regime et de la
Revolution_ (2 vols., Paris, 1885); Susane, _La Tactique financiere de
Calonne_, with bibliography (Paris, 1902).

CALORESCENCE (from the Lat. _calor_, heat), a term invented by John
Tyndall to describe an optical phenomenon, the essential feature of
which is the conversion of rays belonging to the dark infra-red portion
of the spectrum into the more refrangible visible rays, i.e. heat rays
into rays of light. Such a transformation had not previously been
observed, although the converse phenomenon, i.e. the conversion of short
waves of light into longer or less refrangible waves, had been shown by
Sir G.G. Stokes to occur in fluorescent bodies. Tyndall's experiments,
however, were carried out on quite different lines, and have nothing to
do with fluorescence (q.v.). His method was to sift out the long dark
waves which are associated with the short visible waves constituting the
light of the sun or of the electric arc and to concentrate the former to
a focus. If the eye was placed at the focus, no sensation of light was
observed, although small pieces of charcoal or blackened platinum foil
were immediately raised to incandescence, thus giving rise to visible
rays.

The experiment is more easily carried out with the electric light than
with sunlight, as the former contains a smaller proportion of visible
rays. According to Tyndall, 90% of the radiation from the electric arc
is non-luminous. The arc being struck in the usual way between two
carbons, a concave mirror, placed close behind it, caused a large part
of the radiation to be directed through an aperture in the camera and
concentrated to a focus outside. In front of the aperture were placed a
plate of transparent rock-salt, and a flat cell of thin glass containing
a solution of iodine in carbon bisulphide. Both rock-salt and carbon
bisulphide are extremely transparent to the luminous and also to the
infra-red rays The iodine in the solution, however, has the property of
absorbing the luminous rays, while transmitting the infra-red rays
copiously, so that in sufficient thicknesses the solution appears nearly
black. Owing to the inflammable nature of carbon bisulphide, the plate
of rock-salt was found to be hardly a sufficient protection, and Tyndall
surrounded the iodine cell with an annular vessel through which cold
water was made to flow