Intelligence and Miscellaneous Articles. 463 
miles. It will be interesting to learn whether any corresponding 
magnetic twitch appears on the magnetometer records. — Silliman's 
American Journal, November 1883. 
THE FLUOKESCENCE OF IODINE VAPOUK. BY E. LOMMEL. 
Fluorescence has hitherto only been observed in solids and 
liquids. It is an interesting question whether gaseous bodies are 
not also susceptible of fluorescence. 
In order to approach the question, I have made a few prelimi- 
nary experiments in this direction with some of the more power- 
fully absorbing gases and vapours, especially hyponitric acid, 
chlorine, and the vapours of bromine, iodine, and sulphur. 
It was found that iodine vapour has a pronounced orange-yellow 
fluorescence. This is easily observed when sunlight concentrated 
by a lens is allowed to fall on a flask containing vapour of iodine 
which is not too dense. The orange-yellow pencil of light is par- 
ticularly marked when the exciting light has passed through a 
green glass. If a blue glass is used as filter for the rays, the fluo- 
rescence is only feeble; while with red glass it disappears altogether. 
Of the pure spectral colours, the most active were the green 
rays on each side of the line E ; the yellow and bluish green were 
less so; and the red, blue, violet, and ultra-violet were quite in- 
active — a result which was to be expected, from the well-known 
absorptive properties of iodine vapour. 
In order to ascertain whether the ultra-violet rays were active, 
the spectrum was produced by means of apparatus of quartz ; and 
after it had been ascertained that this part of the spectrum could 
not excite fluorescence of iodine vapour, it was also confirmed 
that iodine vapour does not absorb either the ultra-violet, the blue, 
or the violet to any appreciable extent ; for the very highly luminous 
ultra-violet part of the spectrum received on solution of esculine, 
remained unchanged when dense violet vapours of iodine were libe- 
rated in a test-tube held in front of the slit. 
Hence iodine vapour is the only fluorescenfysubstance yet known 
in which the violet and ultra-violet rays are quite inactive. 
The feebly luminous spectrum of the orange-yellow fluorescent 
light is seen to be composed of red, orange, yellow, and green, 
extends from the division 35 of Bunsen's scale to about 60, and is 
brightest in orange. It appeared continuous, without lighter and 
darker lines. 
Solutions of iodine in bisulphide of carbon and alcohol exhibited 
none of the fluorescence characteristic of iodine. It has already been 
stated that solid iodine does not fluoresce. 
I was unable to recognize any fluorescence in the gases and 
vapours mentioned above. — Wiedemann's Annalen, 1883, No. 6, 
p. 356. 
