5296 M. Frauenhofer on the Existence of numerous 
Into a dark room, and through a narrow vertical aperture in 
the window-shutter, about 15" broad, and 36" high, I introduced 
the rays of the sun upon a prism of flint-glass placed upon the 
theodolite. This instrument was 524 feet from the window, and 
the angle of the prism was nearly 60°. The prism was placed 
before the object-glass of the telescope, so that the angles of in- 
cidence and emergence were equal. In looking at this spectrum 
for the bright line, which I had discovered in a spectrum of artificial 
light, I discovered, instead of this line, an infinite number of 
vertical lines of different thicknesses. These lines are darker than 
the rest of the spectrum, and some of them appear entirely 
black. When the prism was turned, so that the angle of inci- 
dence increased, these lines disappeared ; and the same thing 
happened when the angle was diminished. If the telescope was 
considerably shortened, these lines re-appeared at a greater angle 
of incidence ; and at a smaller angle of incidence, the eye-glass re- 
quired to be pulled much farther out, in order to perceive the 
lines. If the eye-glass had the position proper for seeing dis- 
tinctly the lines in the red space, it was necessary to push it in 
to see the lines in the violet space. If the aperture by which the 
rays entered was enlarged, the finest lines were not easily seen, 
and they disappeared entirely when the aperture was about 40". 
If it exceeded a minute, the largest lines could scarcely be seen. 
The distances of these lines and their relative proportions suf- 
fered no change, either by changing the aperture in the shutter, 
or varying the distance of the theodolite. The refracting me- 
dium of which the prism is made, and the size of its angle, did 
not prevent the lines from being always seen. They only be- 
came stronger or weaker, and were consequently more or less 
easily distinguished in proportion to the size of the spectrum. 
The proportion even of these lines to one another appeared to be 
the same for all refracting substances ; so that one line is found 
only in the blue, another only in the red, and hence it is easy 
to recognise those which we are observing. The spectrum formed 
by the ordinary and extraordinary pencils of calcareous spar 
exhibit the same lines. The strongest lines do not bound the 
different colours of the spectrum, for the same colour is almost 
always found on both sides of a line, and the transition from one 
colour to another is scarcely sensible. 
