297 
lines crossing the Spectrum. 
Fig. 5. * shews the spectrum with the lines such as they are 
actually observed. It is, however, impossible to express on this 
scale all the lines and the modifications of their size. At the 
point A the red nearly terminates, and the violet at I. On either 
side we cannot define with certainty the limits of these colours, 
which, however, appear more distinctly in the red than in the 
violet. If the light of an illuminated cloud falls through the 
aperture on the prism, the spectrum appears to be bounded on 
one side between G and H, and on the other at B. The light 
of the sun*, too, of great intensity, and reflected by a heliostate, 
lengthens the spectrum almost one-half. In order, however, to 
observe this great elongation, the light between C and G must 
not reach the eye, because the impression of that which comes 
from the extremities of the spectrum is so weak as to be extin- 
guished by that of the middle of the spectrum. At A, we ob- 
serve distinctly a well-defined line. This, however, is not the 
boundary of the red , which still extends beyond it. At a , there 
is a mass of lines, forming together a band darker than the ad- 
jacent parts. The line at B is very distinct, and of a consider- 
able thickness. From C to D may be reckoned 9 very delicate 
and well-defined lines. The line at C is broad, and black like 
D. Between C and D are found neatly SO very fine lines, 
which, however, with the exception of 2, cannot be perceived, 
but with a high magnifying power, and with prisms of great 
dispersion ; they are besides well-defined. The same is the case 
with the lines between B and C. The line D consists of two 
strong lines, separated by a bright one. Between D and E we 
recognise about 84 lines of different sizes. That at E consists 
of several lines, of which the middle one is the strongest. From 
E to h there are nearly 24 lines. At h there are three very strong 
ones, two of which are separated by a fine and clear line. They 
are among the strongest in the spectrum. The space b F con- 
tains nearly 52 lines, of which F is very strong. Between F and 
G there are about 185 lines of different sizes. At G many lines 
are accumulated, several of which are remarkable for their size. 
From G to H there are nearly 190 different lines. The two 
* We have reduced this figure greatly, and inserted only. a few of the moat 
prominent lines. 
