CO SS ee 
TRANSACTIONS OF SECTION B. 455 
The following Papers were read :— 
1. On Sun-spots and the Chemical Elements in the Sun. 
By Professors Dewar and Liverna. 
The authors take as the text of this paper the spectroscopic observations of sun 
spots made at Greenwich. They point out that 1t does not of necessity follow, 
because a spot is less luminous than the photosphere, that its temperature must be 
less, inasmuch as the radiation of short wave-length generally increases most rapidly 
with the increase of temperature; and the spectra of the vapours of some of the 
metals most abundant in the sun, such as iron and magnesium, are stronger in the 
ultra-violet than in the visible part of the spectrum. They remark that the unequal 
widening of the Fraunhofer lines in spots is analogous to the behaviour of terrestrial 
elements, which give lines of which some are far more readily expanded than others 
by increasing the density of the vapour. They show that there is little reason for 
supposing that the dark lines which are peculiar to spots are due to elements which 
are not to be found on the earth, because the spectra of our chemicals have as yet 
been very partially examined ; and they have found in a cursory examination of the 
arc, while cerium and titanium are introduced into it, that a very great number of 
new lines make their appearance, of which some show coincidences with dark lines 
of spots too striking to be merely accidental. The disappearance of some Fraun- 
hofer lines from spots they attribute, as others have done, to the emission of the 
upper regions of the sun’s atmosphere balancing the absorption below; and they 
point out that the rays for which this happens are the rays which belong to vapour 
of small tension, corresponding to Mr. Lockyer’s long lines—rays which should be 
emitted by the elements in their least complex state of aggregation. The singular 
ray with wave-length 4923, which is a line of iron of high vapour-tension, but 
behaves in the sun as a line of low vapour-tension, being frequently seen high up 
in the solar storms and disappearing from spots, they think must belong to some 
other metal as well as to iron. At the same time they point out that though the 
vapours in the upper regions of the solar atmosphere are generally of very low 
tension, yet they may locally be much denser when solid matters from the coronal 
region fall into the sun and are vapourised in passing through his atmosphere. 
2. Colouring Matters of the Diazo-Group.} 
By Rargaet Metpots, F.1.C., F.C.8. 
The author commenced by giving a sketch of the history of these compounds, 
which were first discovered by Griess, and have since been largely investigated 
owing to their great value as technical products. The diazo-group consists of two 
nitrogen atoms linked together, -N=N-—, and, in accordance with the nomen- 
clature proposed by Wallach, diazo-compounds may be termed primary, secondary, 
or tertiary, according as they contain one, two, or three diazo-groups. Primary 
compounds have hitherto received the largest share of attention. All the known 
bodies of importance belonging to this group may be referred to the three types :— 
C,H,—-N=N-—C,H, . ; : : : « Azobenzene. 
C,H, -N=N-—-C,,H, : : . . . Benzene-azonaphthalene, 
C,,H, -N=N-C,,H, 5 ; : . . Azonaphthalene. 
The general formula is 
R-N=N-R, 
Colouring matters are produced when one or both radicals contain acid or basic 
substituents. 
Secondary compounds are formed on two types, viz. : 
N=N-R N=N-R 
R<yN_N_Pph and Ph<N_N_R 
18 Il. 
} Published in eatenso in the Journal of the Chemical Society, ‘Transactions, 
November 1883, p. 425. 
