432 ME. J. N. LOCKYEE ON SPECTEOSCOPIC OBSEEYATIONS OE THE SUN. 
gators point out the effect of temperature on the different spectra, the temperature cf 
the discharge of Ruhmkorff’s induction-coil being increased by increasing the power of 
the inducing current, or, preferably, by diminishing the duration of the induced one, by 
means of the Leyden jar. 
Among the important results obtained in the case of nitrogen were the following. 
With increase of temperature the light passes through the following colours : — 
Golden, 
Bluish violet, 
White, 
and at an extreme temperature the lines expand, approaching thus to a continuous spec- 
trum. 
We now come to hydrogen. When a Geissler’s tube filled with extremely rare- 
fied hydrogen is used, the spectrum produced by a spark of low temperature consists of 
three lines of the same width as the slit — one red, another bluish green, another violet* ; 
these are respectively termed Ha, H/3, and Hy by MM. Plucker and PIittorf. The 
places of these lines in the solar spectrum are at C, at F, and one at some distance 
from G towards F. 
I quote the following results of increase of temperature from the memoir under 
notice. 
“ Hydrogen shows in the most striking way the expansion of its spectral lines, and 
their gradual transformation into a continuous spectrum. When the direct discharge of 
Ruhmkorff’s large induction-coil is sent even through the old spectrum-tubes enclosing 
hydrogen, the formerly obtained spectrum is essentially altered. By increasing the power 
of the coil, the violet line Hy first expands ; while it continues to expand, the expansion 
of the bluish-green line H/3 becomes visible. Let the aperture of the slit be regulated 
so that the double sodium-line will separate into two single lines nearly touching one 
another. Then, the angular breadth of H/3 becoming two or three minutes, the breadth 
of Hy is about double. The expansion takes place as well towards the less as towards 
the more refracted part of the spectrum. Ha remains almost unchanged after Hy has 
passed into an undetermined large violet band, and H/3 extended its decreasing light on 
its two sides. On employing the Leyden jar, and giving to the gas in our new tubes a 
tension of about 60 millims., the spectrum is already transformed into a continuous one, 
with a red line at one of its extremities. At a tension of 360 millims. the continuous 
spectrum is highly increased in intensity, while the red line Ha, expanded into a band, 
scarcely rises from it. If the electric spark passes through hydrogen at the ordinarv 
tension, the ignited gas on its way always gives the spectrum of the three expanded 
lines. 
“ Even in the old spectral tubes enclosing highly rarefied hydrogen, the ground, from 
which the three characteristic lines rise, did not appear always of the same darkness ; 
in some instances new bright lines appeared, especially in the neighbourhood of the sodium - 
* I am aware that Angstrom has discovered another line, but it is not necessary here to consider it. 
