710 
MR. W. CROOKES OK RADIANT MATTER SPECTROSCOPY. 
phosphorescence appeared. The spectrum consists of a faint band in the red, then a 
sharp orange line (146, 165), next a wide ill-defined orange band, and finally an 
equally ill-defined green band. The appearance is shown in fig. 3. 
138. When, however the samaria is mixed with lime (114) before examination in 
the radiant matter tube, the change is very striking, and the spectrum is, if any¬ 
thing, more beautiful than that of yttrium. The bands are not so numerous, but the 
contrasts are sharper. Examined with a somewhat broad slit, and disregarding the 
fainter bands, which require care to bring them out, the spectrum is seen to consist of 
three bright bands,—red, orange, and green,—nearly equidistant, the orange being the 
brightest. With a narrower slit the orange and green bands are seen to be double, 
and on closer examination faint wings are seen, like shadows to the orange and green 
bands. In this spectrum the sharp orange-coloured line (137) of pure samaric sulphate 
is absent. 
139. The bands are best seen in a spectroscope of low dispersion, and with not too 
narrow a slit. In appearance they are more analogous to the absorption bands seen in 
solutions of didymium than to the lines given by spark spectra. Examined with a 
high magnifying power all appearance of sharpness generally disappears : the scale 
measurements given below must therefore be looked upon as approximate only; the 
centre of each band may be taken as accurately determined within the unavoidable 
errors of experiment, but it is impossible to define their edges with much precision. 
140. The accompanying cut (fig. 4) gives as good an idea of the spectrum of 
Fig. 4. 
samarium-calcium as is possible in black and white. The numbers along the top are 
the squared reciprocals of wave-lengths, and are on the same scale as the diagram 
of the yttrium spectrum (71) given in my Bakerian Lecture already quoted. The 
phosphorescing mixture in the tube consisted of 20 parts of pure samaria and 80 parts of 
lime. They were converted into nitrates in a platinum capsule, and then decomposed 
by excess of sulphuric acid and ignited at a dull red heat. If sulphuric acid is added 
in the first instance there is a difficulty in getting the earths completely converted. 
The least refrangible band seen is a very faint red, which extends from ^ 2310 to 
2400. Here a much stronger red band begins extending to 2494. The first 
component of the bright orange band begins at 2739 and ends at 2762. Between 
2762 and 2798 is a dark interval, and then the second component of the orange band 
