IN CONNEXION WITH THE SPECTRUM OF THE SUN. 
641 
the poles, and the spark was then passed, the induction-coil already mentioned being 
used. When it was desired simply to observe the spark in air, the hydrogen apparatus 
was disconnected, or the poles were placed in an ordinary spark-stand. 
Besults of Experiments. 
The following are the results of some experiments made with the spark in air, the 
jar being thrown out of the circuit. 
Lead. 
Plumbic Fluoride , Pb F 2 . — It will be seen on referring to the map of this spectrum 
(Plate LI.) that the eleven longest lines of the following wave-lengths*, 4167*5, 4246*0, 
4386-5, 5163-0, 5372-0, 5523-5, 5546-0, 5607-0, 6040-0, 6059-0, and 6452-0, were seen. 
Of these it is to be remarked that 4246-0 and 4386’5 are only seen for a short time 
when the spark first begins to pass, 6452-0 is very faint, and 5523-5 very short; so that 
practically the spectrum contains but seven distinctly visible lines. 
Plumbic Chloride, Pb Cl 2 . — On observing the spectrum of this salt, it is found to have 
been simplified in the following manner : — 
The lines left are 4167*5, 5163-0, 5372-0, 5523-5, 5546-0, 5607-0, 6040-0, 6059-0, and 
6452-0, nine in number ; 5523'5 has become excessively short, and 6452-0 rather brighter 
than it was in the fluoride. 
Plumbic Bromide, Pb Br 2 . — 4167*5 still maintains its brilliancy undimmed, 5163 - 0, 
5372-0, 5546-0, and 5607*0 remain; 5523-5 is just distinguishable as a dot on the pole, 
but 6040-0, 6059-0, and 6452-0 are completely lost, the spectrum thus being reduced to 
five lines. 
Plumbic Iodide, Pb I 2 . — 4167‘5 is little or not at all altered in appearance, 5163-0, 
5372-0, 5607-0 yet remain ; 5546-0 has become a dot, and faint indications of 5523-5, in 
the same state but much fainter, are visible. 
The composition 
by weight 
of 
these compounds 
is as follows : — 
Pb F 2 , 
Pb 
to F . 
1-0 
to 0-18 
Pb Cl 2 , 
Pb 
„ Cl . . . . 
1-0 
„ 0-34 
Pb Br 2 , 
Pb 
„ Br . . . . 
1-0 
„ 0-77 
Pb I 2 , 
Pb 
„ I • • • . 
1-0 
„ 1-22 
If these results 
are expressed 
in another way, by making the 
unity, we have : — 
Pb F 2 , 
F 
to Pb . . . 
1-0 
to 5-4 
Pb Cl 2 , 
Cl 
„ Pb . . . 
1-0 
„ 2-9 
Pb Br 2 , 
Br 
„ Pb . . . 
1-0 
„ L2 
Pb I 2 , 
I 
„ Pb . . . . 
1-0 
„ 0-8 
Now the lines in 
the specti 
um 
of lead increase 
in length and 
the above series, i. e. as the percentage weight of lead increases, as is shown in the second 
* From Thal£n’s observations. 
4 e 2 
