14 
DES. J. PLtJCKEE ANT) J. W. HITTOEF ON THE 
by a blowpipe. The direct charge of Ruhmkorff’s large induction coil sent through it, 
generally indicates by their spectra traces of remaining foreign substances (8). But 
when the tube was heated by a small alcohol-lamp, at a certain moment a fine sulphur- 
spectrum of the first order appeared, undisturbed by any former spectrum. The beauty 
of the spectrum increased when we continued to heat moderately. 
36. We counted thirty-seven well-defined bands, extending nearly from Ha to Hy. 
Seven of these bands, the first of which was of a dark-red colour and visible only under 
favourable circumstances, preceded the sodium-line, eighteen fell between this line and 
H/3, and eleven between H/3 and Hy, the last of which being broader, appears some- 
times divided into two. After a last band, traversed by Hy, a larger and strongly 
shaded space extended towards the extreme violet. The breadth of the bands 
increased from the less to the more refracted part of the spectrum. In each band, 
contrary to what takes place in the case of nitrogen, namely, with regard to its chan- 
neled spectrum, the shading produced by fine dark lines decreases from the less to the 
more refracted extremity. The darkest part of the shadow is bounded by a small sepa- 
rate band of a varied appearance, generally formed by two small bright lines including 
a somewhat larger dark one. By these small bands the purely channeled character of 
the spectrum is disturbed. 
37. If, while the discharge is passing, we continue to heat the tube by a lamp, the 
brightness of the spectrum always increases ; but if we approached to a certain degree of 
temperature, in different parts of the spectrum we have described, bright-coloured lines 
belonging to the sulphur-spectrum of the second order appeared and disappeared again 
according to the fluctuating heat, till at last the second of the two rival spectra remained 
undisturbed. The colour of the light was changed. In cooling again after the lamp 
was taken off, the light within the tube changed its colour again, while the spectrum of 
the second order was replaced by the spectrum of the first order. 
There is a certain elevation of temperature at which the increased density of the 
vapour does not permit the discharge to pass ; the light within the tube is extinguished, 
but abruptly reappears after cooling. 
38. Well-defined bright lines, constituting a fine sulphur-spectrum of the second 
order, are obtained if moderate discharges of Rhumkoeff’s large induction coil are sent 
through the tube, the tube being slightly heated by means of an alcohol-lamp, and a 
small Leyden jar being intercalated. At first the spectrum extends only from about the 
sodium-line to H/3. One observes chiefly a characteristic group of sixteen lines, followed 
at some distance by two separate lines. The spectrum once developed persists even after 
taking off the lamp. When we continue to heat, the brightness of the group increases 
and its lines begin to expand, while at the same time the hitherto black ground is 
coloured. The brilliancy may be increased to such an extent as to be unbearable to 
the eye. Beyond the sodium-line, towards the red extremity, new distinct lines appear, 
among which we particularly distinguish a triple line, remarkable as well for its fine 
red colour as for its distinctness, and nearer to Ha a second such triple line, at first well 
