MR. W. CROOKES OK RADIANT MATTER SPECTROSCOPY. 
711 
is seen extending from 2798 to 2818. This band is stronger and more sharply defined 
than the preceding band. A faint yellow wing extends from the second orange band 
to 2942. There is now an intensely black interval reaching to 3025 ; here a faint 
yellowish-green light is seen extending to 3149, where the green band commences 
and extends to 3164. Here a fainter green wing begins, and extends to 3270. On 
this wing a very narrow faint green band is seen, having its centre at 3190. There is 
then another dark space, after which three ill-defined blue and violet bands are seen, 
too faint to measure accurately. 
141. Preliminary experiments (114) had shown me that lime was one of the best 
materials to mix with samaria in order to bring out its phosphorescent spectrum, but 
it was by no means the only body which would have the desired effect. More 
accurate observations were now taken with pure materials mixed together in definite 
quantities. The bodies employed were those enumerated in par. 113. Of these the 
following induced no phosphorescence :—zirconium, cerium, didymium, copper, silver, 
manganese, and tin ; silicic, titanic, tungstic, molybdic, niobic, and tantalic acids. 
142. The other substances which I tried caused the samarium to give good 
phosphorescence with a discontinuous spectrum. There is a general resemblance 
between these spectra, but nearly all of them differ one from another in details. In 
the following descriptions I will take the calcium-samarium spectrum (140) as the 
standard of comparison:— 
Strontium and barium, when mixed with samarium, give almost identical spectra ; 
the red band is similar to the one produced by calcium, but the orange bands have 
become a blurred orange space, with outline ill-defined on the side towards the red, 
and sharper at the more refrangible side. There is no trace of division in the orange 
space ; but the green, which with calcium is narrow and single, becomes with barium 
and strontium a well-defined luminous double green band, with a sharp black 
separating interval. 
Beryllium and samarium give a very faint phosphorescent spectrum, consisting of a 
red, orange, and green band only ; the green occupying the position of the second 
green band given by calcium-samarium. 
143. Thorium and samarium give a very similar spectrum to the one produced by 
barium or strontium with samarium, a slight difference being observable in the orange, 
which shows signs of separation into two components. 
Thorium, as oxide or sulphate, by itself gives no phosphorescence (26, 28), and in 
fact, as I have already shown, renders the vacuum tube non-conducting ;* samaria 
* “ This earth is, however, remarkable for its very strong attraction for the residual gas in the 
vacuum tube. On putting thorina in a tube furnished with well-insulated poles, whose ends are about 
a millimetre apart in the centre, and heating strongly during exhaustion, the earth, on cooling, absorbs 
the residual gas with such avidity that the tube becomes non-conducting, the spark preferring to pass 
several inches in air rather than strike across the space of a millimetre separating the two poles.”—Proc. 
Roy. Soc., No. 213, 1881, Yol. XXXII., p. 209. 
4 Y 2 
