39 
^ drff'erent Species of Glass. 
out any illusion in the spectrum of the light of Sirius, three 
large lines, which apparently have no resemblance with those of 
the sun’s light. One of them is in the green, and two in the 
blue space. Lines are also seen in the spectrum of other fixed 
stars of the first magnitude ; but these stars appear to be diffe- 
rent from one another in relation to these lines. As the object- 
glass of the telescope of the theodolite has only 13 lines of aper- 
ture, these experiments may be repeated, with greater precision, 
by means of an object-glass of greater dimensions. 
The electric; light is, in relation to the dines of the spectrum, 
very different from the light of the sun and of a lamp. ^In this 
spectrum, we meet with several lines, partly very clear, and one 
of which, in the green space, seems very brilliant, compared with 
the other parts of the spectrum. Another line, which is not 
quite so bright, is in the orange, and appears to be of the same 
colour as that in the spectrum of the light of a lamp; but, in 
-measuring its angle of refraction, I find that its light is much 
more strongly refracted, and nearly as much as the yellow rays 
of the light of a lamp. Towards the extremity of the spectrum 
we perceive in the red a line of very little . brightness,; yet its 
light has the same refrangibility as that of the clear dine of the 
'light of a lamp. In the rest of the spectrum we niay still easily 
distinguish other four lines sufficiently bright 
In making the light of a lamp fall through a marrow aperture, 
from 15" to 30" wide, upon a prism of great dispersion, placed 
"before the telescope, we perceive that the red line of this spec- 
trum is formed by two very delicate bright, lines, similar in size 
and in distance to the two dark lines D, Fig. V. Plate VIL' 
‘Whether the aperture through which the light of the lamp passes 
'is wide or narrow, if we cover the point of the flame, and the 
lower blue extremity of it, the red line appears less clear, and is 
-more difficult to be distinguished. Hence it appears that this 
line derives its origin principally from the light of the two extre- 
mities of the flame, particularly the inferior one. 
* In order to obtain a continuous electrical light, I brought' to- within half an 
inch of each other, two conductors, and I united them by a very fine glass thread. 
One of the two was connected with an electrical machine, and the other communi- 
x:*ated with the ground. In this manner, the light appeared to pass continuously 
along the glass fibre, which consequently formed a fine and brilliant line of light. 
