A. W. Wright—Spectrum of the Zodiacal Light. 43 
point of greatest intensity lying between 70 and 80, and evi- 
dently nearer the former. Similar results were obtained with 
twilight, the lower and upper limits, obtained with a slit cover- 
ing two divisions, being 50 and 184°6, respectively. The lower 
—e in each case were corrected by adding the breadth of the 
sit. 
The accompanying plate exhibits the general character of the 
zodiacal spectrum, and its relation to those with which com- 
parison was made. The corresponding portion of the solar 
spectrum, with a few of the principal Fraunhofer lines, is rep- 
resented at the bottom, as a standard of reference, and to show 
the position and value of the divisions of the scale used in the 
instrument, the numbers of which are placed above the lines. 
The band between 50 and 60, marked 6, is atmospheric, and its 
place is determined from Prof. Angstrém’s chart, and from Dr. 
Janssen’s diagram of the telluric lines. It is the band seen on 
several occasions when a very narrow slit was used, as mentioned 
below. The line marked ais the principal line of the auroral 
spectrum, sometimes referred to the zodiacal spectrum, as stated 
in a previous paragraph. ‘The wave-lengths, corresponding to 
points in the spectroscopic scale, for intervals of five divisions, 
are given in the following table. 
Scale Wave-length. Scale Wave-length. Scale Wave-length, 
No. No. No, 
40 6255 75 5216 110 4606 
45 6064 80 6111 115 4538 
50 5889 85 5012 120 4472 
55 5726 90 4919 125 4409 
60 5583 95 4831 130 4352 
65 5451 100 4751 135 4298 
70 5329 105 4677 140 4246 
was observed, that when diffused sunlight is directly observed 
with the spectroscope, and simply weakened by narrowing the 
slit, the maximum is near 50 of the scale. The apparent ex- 
* Monthly Notices of the Royal Ast. Soc., June, 1872, P. 277. 
