16 
DES. J. PLtJCKEE AND J. W. HITTOEF ON THE 
pounds of carbon) ; the group f is very faint, the group g beautifully violet, h rather 
ultra-violet. 
43. The whole spectrum, except its red extremity, is divided into large shaded fields. 
The shadow increases from the less to the more refracted part of each field ; from its 
Drighter less refracted part arise the bright lines of one group, the first of these lines 
towards the darkest extremity of the preceding field. As well as in the former cases of 
nitrogen and sulphur, the shadow is produced by dark transversal lines on a coloured 
ground. But here the distance of the shading-lines from each other varies even in the 
same field. Towards the bright, i. e. the less refracted extremity of each field, the 
distance decreases, while at the same time the darkness and the breadth of the lines 
is diminished. The space between two consecutive lines appeared to be greatest in the 
field containing the group c, at a distance from d about twice as great as that from c. 
There we counted, on making use of two prisms and applying a magnifying-power of 
eighteen, the aperture of the slit being regulated in the ordinary way (13), nine shading- 
lines, including eight nearly equal small bands, the total breadth of which corresponded 
to five divisions of our arbitrary scale. Hence we computed the angular distance of 
two consecutive dark lines which we observed to be about five-fourths of the distance of 
the sodium-lines. 
The dark shading-lines also appear within the bands bounded by the lines of the 
brighter characteristic groups. The band between the second and the third bright line 
of the yellow group b, the total breadth of which corresponds to four divisions of our 
arbitrary scale, was divided by dark lines into twelve smaller bands of about equal 
breadth. Accordingly the angular distance of two such consecutive lines is about two- 
thirds the distance of the two sodium-lines. The dark lines within the neighbouring 
band, bounded by the first and second bright line of the same group, were much nearer 
to one another, and their number too great to be counted with certainty. 
44. Between the groups f and g there is indicated a particular distribution of light 
and shadow, which, being a faint copy of what takes place if olefiant gas be burned 
instead of cyanogen, will be better understood after we have described the spectrum of 
the new gas. 
45. The least-refracted part of the spectrum, preceding the first line of the group a , 
essentially differs from the more refracted part already described. There are three fine 
red bands contiguous to the first bright line of the group, extending nearly to Ha, and 
beyond this hydrogen-line, after a dark space, two similar but not so well-defined bands. 
The breadth of these bands is nearly the same, and all are shaded in a similar way. 
Contrary to the distribution of shadow in the larger field, the shadow is strongest in the 
less refracted part of each band ; in the most refracted part we observed two bright lines. 
46. When the combustion of cyanogen took place in air, the bands we have just 
described were best developed, and new similar ones added. They extended from beyond 
Ha nearly to H/3. The breadth of these bands slightly increases towards the violet end 
of the spectrum, their general description remaining the same. We especially counted 
seven such bands, the first of which is traversed by the double sodium-line, and the last 
