OF THE SOLAR SPECTRUM. 553 
the spectrum, we expose it during some seconds to the solar rays, 
or to the diffused light; this surface is then luminous in all its 
extent; but by projecting the spectrum during some minutes, 
reshutting the aperture of the shutter, then again looking at the 
surface, we see that it has remained luminous, with the exception 
_ of the part u v, which has become perfectly dark, and of the two 
parts « 8, y 8, which have increased in intensity. This part, p », 
therefore contains rays which act in an opposite manner to the 
others, and which destroy the phosphorescence; besides, if we 
raise the temperature of this surface by heating the paper with 
aspirit lamp, all the parts previously brilliant acquire, by ele- 
_vating the temperature, an exceedingly vivid phosphorescence, 
fi whilst the part %» remains completely dark. 
_ Thus the rays contained in this latter part not only take away 
_ the phosphorescence from the molecules, but they also completely 
_ destroy this faculty, so that, by the elevation of temperature, the 
"parts on which these rays fall are no longer phosphorescent. 
ese rays, with respect to the sulphuret of calcium, at their least 
degree of refrangibility begin between G and H, but nearer to 
—G, and extend as far as vy beyond A. By the help of screens 
these latter rays may be rendered evident. 
We know that glass coloured red by means of the protoxide 
‘of copper allows only red and orange-coloured luminous rays, 
and the chemical rays which accompany them, to pass; it was 
therefore natural to suppose that this glass would only let pass 
rays which act to destroy phosphorescence ; and this in fact is 
peat I have verified. If we take a sheet of paper prepared as 
before with a layer of powder of sulphuret of calcium, if we ex- 
pose it to the light of day and bring it back into darkness, it will 
then be luminous; but placing immediately on this surface a card 
which only covers a certain part of it, then above a red glass, and . 
again exposing the whole to the action of the solar rays during a 
“minute at most, if we afterwards look at the paper in the dark, 
we see that all the part which had been sheltered from the action 
: of the rays which have passed through the red glass is still very 
brilliant, whilst the remainder of the surface is become dark, 
‘The rays which pass through the red glass possess the property 
of destroying phosphorescence, as in the least refrangible parts 
| of the spectrum ; and we cannot say that they are the calorific 
| Tays, since these rays, on the contrary, possess the property of 
| 
| agen the luminous faculty of bodies. 
In the same manner I examined the action of the spectrum on 
