130 REPORTS ON THE STATE OF SCIENCE. 
it in the green or in the blue, sometimes even in the yellow. I never 
observed that a chief-spectrum passes the wave-length of 460. The 
chief-spectra consist of narrow-channelled bands, which nearly always 
have their sharper boundary toward the violet end of the spectrum. 
The number of the bands varies within a wide range for the different 
substances between a few strips and several dozen. The distances 
between them appear generally irregular. The substances, when they 
send out their chief-spectrum, look red or yellow or green, or of any 
other tint which occurs with fluorescent minerals or inorganic salts. 
On the other hand, the light which is emitted during the first 
moments of radiation and belongs to the initial-spectrum is—at least, 
for colourless substances—always blue. The discontinuous iitial- 
spectra of two substances are, like their chief-spectra, never quite 
the same, but as in their general appearance they are rather similar to 
each other, at least in the visible part of the spectrum, so one cannot 
recognise a substance at a glance by its initial-spectrum as one can 
by the chief-spectrum, but measures of its wave-lengths are neces- 
sary. The initial-spectra begin always like the chief-spectra in the 
red, but not only reach into the green or blue, but go on into the 
ultra-violet. One type of initial spectra occurring especially frequently 
invariably consists of siz groups of bands. Hach of the six groups is - 
formed by the same number of strips at the same relative distance and 
intensity; and as the relative distance of the groups themselves is also 
not very different—at least in the prismatic spectrum—the whole spec- 
trum gives the impression of having a very high regularity. Such 
spectra, consisting of six groups, with different wave-lengths for each 
individual substance, are, for example, the initial-spectra of mesitylenic 
acid, of metatoluic acid, of the anhydride of benzoic acid, of toluene and 
of its halogen substituted derivates—and of many other substances, 
especially of those aromatic bodies whose molecules contain a single- 
ring group. 
In the groups which contain two or even more benzene rings, and 
especially in condensed substances, one finds also other types of initial- 
spectra, all extending from red into the ultra-violet, which I will not 
speak of in this short report. 
The third spectrum of aromatic compounds is shown in very charac- 
teristic forms especially by dissolved compounds of the condensed type ; 
for instance, by naphthalene and most of its derivates. The chief 
spectrum of naphthalene shows the wave-lengths 
589 (very bright) 589 (very bright) 
555 615 (probably a doublet) 
560 630 
573 648 
} 539 and 589 mark sharp boundaries on the violet side, the other wave- 
lengths belong to the middle of narrow strips. 
The spectrum of the same naphthalene, if dissolved in monochloro- 
benzene (which itself gives only a faint and almost continuous spectrum) 
shows the following wave-lengths (all for the middle of the narrow 
strips) :— 
517\ 
473) 3 505 | nother brie ES ist) Pu oe 
483 } bright ait rather bright 528 { rather faint 5451 565 rather faint 
582 faint. 
