76 Scientific Intelligence. 
In December, 1872, I compared this line directly with the first 
line in the spectrum of the Great Nebule in Orion. I was de- 
lighted to find this line sufficiently coincident in position to serve 
as a fiducial line of comparison. 
not prepared to say that the coincidence is perfect ; on the 
contrary, I believe that if greater prism power could be brought 
to bear upon the nebula, the line in the lead spectrum would be 
found to be in a small degree more refrangible than the line in 
the nebule., 
as a fiducial line in the observations I had in view. 
In m map of the spectrum of lead this line is not given. 
In Thalén’s map (1868) this line is represented by a short line to 
show that, under the conditions of spark under which Thalén ob- 
served, this line was emitted by those portions only of the vapor 
of lead which are close to the electrodes. ; 
I find that by alterations of the character of the spark this line 
long and reaches from electrode to electrode. As some 
due not to the vapor of lead but to some combination of nitrogen 
under the presence of lead vapor. As, however, this line is bright 
imi i is taken in a current of 
need scarcely remark that the cireumstance of making use of 
this line for the purpose of a standard line of comparison is not 
to be taken as affording any evidence in favor of the existence of 
lead in the nebule, 
ne was observed on several nights, so that the whole 
observing time of the past year was devoted to this inquiry. In 
no instance was any change of relative position of the nebular 
line and the lead line detected. 
3 
aie 
td 
