440 
POPULAR SCIENCE REVIEW. 
tribution of Heat amidst and beyond the coloured rays of the 
spectrum (see Heat in the plate). The first spot dries over a 
space which is just below the extreme red ray, thus indicating 
this as the point of maximum calorific power. With gradually 
diminishing intensity, this drying goes on through the spectrum, 
presenting on the paper an image similar to that represented in 
the central figure of the drawing, all indication of Heat ceasing 
in the violet ray. While this result is being obtained over the 
space covered with coloured bands of light, three well-defined 
spots dry out below the red rays where there is no fight. These 
are brought out with greater intensity if a second wash of ether 
be applied. The heat spectrum is thus shown to be of much 
greater length than the light spectrum. 
Sir John Herschel discovered in these extra spectral heat- 
rays some peculiar properties ; they appeared to possess all the 
ordinary properties of dark heat-rays, with some peculiar che- 
mical power superadded ; hence, to distinguish these from the 
ordinary heat-rays, it was proposed that they should be called 
the parathcrmic rays. 
These heat-rays have been investigated by Mrs. Mary Somer- 
ville, and that lady has added some remarkable facts to the 
records of science. If the juices of flowers be expressed, and 
papers stained with them be placed under the action of those 
rays, many very curious results are obtained. Our space will 
admit of our describing one only, and that one is represented 
on our drawing marked fig. 1. In this particular experiment 
the coloured juice of the dark-purple dahlia was washed over 
pure white bibulous paper. This being exposed to the spectrum, 
was gradually changed, over the space occupied, by the parather- 
mic rays, and a brown flame-shaped image was the result, with 
a spot of a dull red a little below it. By continuing the action, 
a peculiar internal action was seen to take place, and eventually 
four spots were formed over the brown space, two of these being 
red and two blue. It would thus appear that we had, by the 
action of these peculiar heat-rays, eliminated the two colours, 
which form, when combined, the purple of the dahlia. 
It might be noted, that if clilorophyl, the green colouring 
matter of leaves, be taken and treated in this way, it is always 
turned brown by the parathermic rays. It is yet more curious 
that, at whatever period of the year we obtain this green 
colouring matter, the resulting brown is always that winch 
marks the autumnal foliage of the plant from which the leaves 
have been gathered. Investigation continued over many years, 
shows that the quantity of these peculiar lieat-rays varies with 
the seasons, and that they are most abundant in the sun’s rays 
in the autumn. We may therefore infer that the ripening of 
fruits and grain, and the autumn tinting of the forest trees, are 
