540 E. BECQUEREL ON THE CONSTITUTION 
The lines A, B, C are in the red and orange; D is at the limit 
of the orange and the yellow; EK and # are in the green; F is in” 
the commencement of the blue; G between the blue and the 
indigo; and H at the end of the violet; but beginning from H 
as far as I, the tint of the light is ashy-gray, and at H it departs 
from the violet tint. The luminous limit of this side is very 
difficult to perceive. 
If we examine the spectra formed by the light of the planets) 
and that of the moon, the same lines are found as with the solar 
light and at the same intervals, which proves that they have the 
same origin; but this is not the case with the stars, such as 
Sirius, &c.: there are indeed black lines, but they are no longer 
the same. These phenomena, which belong to the very nature 
of light, are very interesting to study. 
Artificial lights only afford black lines after having traversed 
differently coloured bodies. We, however, see in their spectra 
one or two brilliant lines towards the yellow, and, in the electric 
light alone, several brilliant lines distributed throughout the 
spectrum. These lines no doubt arise from rays of different 
degrees of refrangibility, which are absorbed by the media 
through which they pass. Fraunhofer operated, as we have 
seen, by receiving on a telescope, which magnified fifteen or 
twenty times, the rays refracted through the flint-glass prism 
placed before the object-glass very near it, and in the position 
of minimum deviation. ; 
They can also be seen by projecting the spectrum on a white 
screen; but as the finest lines cannot then be distinguished, we 
shall point out the manner of operating in order to study them, 
haying ourselves had occasion to project them upon different 
substances in other experiments, the results of which will here- 
after be given. 
In the path of a solar ray reflected from a mirror and passing 
through a narrow vertical aperture, is placed a very pure prism 
of flint-glass, having its edge vertical, and disposed in the direc- 
tion of the minimum deviation; then immediately behind the 
prism a lens of about one metre in focal length is interposed. 
If the prism is situated at a distance equal to two metres, or 
twice the focal distance of the lens from the aperture, and if a 
white surface is placed at two metres from the prism, then the 
lines of the spectrum will be very well depicted upon its surface. 
Without a converging lens we could not distinguish the lines 
