i88o.] 
Spectrum Analysis. 
737 
leaves “ deflagrated by galvanism.” But a much more im- 
portant— and perhaps, as regards real novelty, the most 
important — series of researches on the subject of the speftia 
of metals adting as dischargers of the eleftnc current was 
published, in the year preceding, by Professor Wheatstone. 
From these researches Mr. Wheatstone inferred that 
eledtric light results from the volatilisation and ignition (not 
combustion) of the ponderable matter of the conductor 
itself and that, as the speftra were altogether different 
according to the nature of the latter, “by this mode of 
investigation [that is, by the analysis of either the eledtro- 
magnetic or voltaic spark] the metals may be readily dis- 
tinguished from each other.” Mr. Wheatstone found also 
that, with the ordinary eledtric spark, the lines of the 
speara were “ different in number and position in every 
metal employed,” without stating, however, whether they 
coincided with those produced by the corresponding sub- 
stances employed as galvanic or eledtro-magnetic electrodes. 
This it would seem important to have remarked on, as the 
author had observed that “ the light which accompanies the 
ordinary combustion of the metals” really gave appear- 
ances totally dissimilar to the above.” After these investi- 
gations nothing of any great importance was brought to 
light concerning the spedtra of sparks. M. Foucault, m 
184.0 made some observations which yielded no remarkable 
results, except one to which we shall have to revert, and 
which was extremely striking, but is not connected with our 
present subjedt. M. Masson, in 185 1 and 1 55? P u ls e 
researches which, however painstaking and elaborate, tended 
rather to confuse than to elucidate the matter in han - 
Much more valuable and highly suggestive was a paper by 
M. Angstrom, published in 1855, who for the first time 
noticed the very interesting fadt that, whilst part of the lines 
of the speftra of sparks belonged to the metals which formed 
the elearodes, others were of aerial origin, and could con- 
sequently be varied according to the nature of the gaseous 
medium in which the discharge was taken. This faa was 
noticed at about the same time in America by Mr. Alter, and 
was further investigated in 1858 by M. Van her Willigen 
whilst the subjea of the speara of the light of exhausted 
tubes filled with gases of extremely small density, and tia- 
versed by induaion-currents,— in other words, of gases made 
glowing by elearicity,— was elaborately examined in 1858-9 
by M. Plucker. . r ,, 
From these various researches, and especially from those 
of Mr. Wheatstone on the metals and of M. Plucker on 
3 A 2 
