ALED TO BY THE SOLAR AND ELECTRIC BEAM
HEAT OF BEAM
COMBUSTION BY TOTAL BEAM AT THE FOCI OF MIRRORS AND LENSES
COMBUSTION THROUGH ICE-LENS
IGNITION OF DIAMOND
SEARCH FOR THE RAYS HERE EFFECTIVE
SIR WILLIAM HERSCHEL'S DISCOVERY OF DARK SOLAR RAYS
INVISIBLE RAYS THE BASIS OF THE VISIBLE
DETACHMENT BY A RAY-FILTER OF THE INVISIBLE RAYS FROM THE VISIBLE
COMBUSTION AT DARK FOCI
CONVERSION OF HEAT-RAYS INTO LIGHT-RAYS
CALORESCENCE
PART PLAYED IN NATURE BY DARK RAYS
IDENTITY OF LIGHT AND RADIANT HEAT
INVISIBLE IMAGES
REFLECTION, REFRACTION, PLANE POLARIZATION, DEPOLARIZATION,
CIRCULAR POLARIZATION, DOUBLE REFRACTION, AND MAGNETIZATION
OF RADIANT HEAT.

Sec. 1. _Range of Vision and of Radiation_.

The first question that we have to consider to-night is this: Is the
eye, as an organ of vision, commensurate with the whole range of solar
radiation--is it capable of receiving visual impressions from all the
rays emitted by the sun? The answer is negative. If we allowed
ourselves to accept for a moment that notion of gradual growth,
amelioration, and ascension, implied by the term _evolution_, we might
fairly conclude that there are stores of visual impressions awaiting
man, far greater than those now in his possession. Ritter discovered
in 1801 that beyond the extreme violet of the spectrum there is a vast
efflux of rays which are totally useless as regards our present powers
of vision. These ultra-violet waves, however, though incompetent to
awaken the optic nerve, can shake asunder the molecules of certain
compound substances on which they impinge, thus producing chemical
decomposition.

But though the blue, violet, and ultra-violet rays can act thus upon
certain substances, the fact is hardly sufficient to entitle them to
the name of 'chemical rays,' which is usually applied to distinguish
them from the other constituents of the spectrum. As regards their
action upon the salts of silver, and many other substances, they may
perhaps merit this title; but in the case of the grandest example of
the chemical action of light--the decomposition of carbonic acid in
the leaves of plants, with which my eminent friend Dr. Draper (now no
more) has so indissolubly associated his name--the yellow rays are
found to be the most active.

There are substances, however, on which the violet and ultra-violet
waves exert a special decomposing power; and, by permitting the
invisible spectrum to fall