HSU ES ESE TEE MURS SF SNENNO Soe se om ME EN Maan SEUSS ER FEE Re ae On ae ee gee ay ee ere ey ee Pe eee ee eee tree eee 
oa ead 
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Nature of the so-called Elements. 1138 
hydrogen lines, being still brilliant, the h line was not present 
(a condition of things which, in all probability, indicated a 
reduction of temperature), calcium began to make itself unmis- 
takably visible; and finally, when the hydrogen lines are 
absent, they become striking objects in the spectrum of the 
corona. 
To come back to A, then, I have shown that Dr. Frankland 
and myself, in 1869, found that it only made its appearance 
when a high tension was employed. We have seen that it was 
ya from among the hydrogen lines during the eclipse of 
1875. 
I have now to strengthen this evidence by the remark that 
it is always the shortest line of hydrogen in the chromosphere. 
now pass to another line of evidence. 
I submit to the Society a photograph of the spectrum of 
indium, in which, as already recorded by Thalén, the strongest 
line is one of the lines of hydrogen (A), the other line of hydro- 
gen (near G) being absent. I have observed the C line in the 
spark produced by the passage of an induced current between 
indium poles in dry air. 
As I am aware how almost impossible it is to render air per- 
fectly dry, I made the following differential experiment. A 
glass tube with two platinum poles about half an inch apart 
was employed. Through this tube a slow current of air was 
driven after passing through a U tube one foot high, containing 
calcium chloride, and then through sulphuric acid in a Wolff’s 
bottle. The spectrum of the spark passing between the plati- 
num electrodes was then observed, a coil with five Grove cells 
and a medium sized jar being employed. Careful notes were 
made of the brilliancy and thickness of the hydrogen lines as 
compared with those of air. This done, a piece of metallic 
indium which was placed loose in the tube, was shaken so that 
one part of it rested against the base of one of the poles, and 
one of its ends at a distance of little less than half an inch 
from the base of the other pole. The spark then passed 
between the indium and the platinum, The red and blue lines 
of hydrogen were then observed both by my friend, Mr. G. W. 
Hemming, Q.C., and myself. Their brilliancy was most mark- 
edly increased. This unmistakable indication of the presence 
of hydrogen, or rather of that form of hydrogen which gives 
us the / line alone associated into that form which gives us the 
blue and red lines, showed us that in the photograpb we were 
not dealing with a physical coincidence, but that in the are this 
Special form of hydrogen had really been present ; that it had 
come from the indium, and that it had registered itself on the 
photographie plate, although ordinary nyuronen persistently 
refuses to do so, Although I was satisfied from former experi- 
