March 3, 1887] 



NA TURE 



At o'ooo875 sec. interval the highest speed the instrument 

 could be revolved with accuracy, 

 the whole of the lines usually 

 seen in the yttria s,:ectruin could 

 he seen of nearly their usual 

 brightness. 

 1 have already recorded (Phil. Trans., 1883, Part HI. 

 p. 914- 16>, that phosphate of yttria, when phosphoresced in 

 laio, gives the green lines very strongly whilst the citron band 

 ;, hazy and faint. The same tube of yttric phosphate was now 

 examined in the phosphoroscope. The green lines of (j/3 soon 

 showed themselves on setting the wheel into rapid rotation, but 

 I was unable to detect the citron band of GS even at a very high 

 speed. 



The effect of calcium on the phosphorescence of yttria and 

 samaria has been frequently referred to in my previous papers. 

 It may save time if I summarise the remits here About i per 

 c«nt. of lime added to a badly phosphorescing body containing 

 yttrium or samarium always causes it to phosphoresce well. It 

 diminishes the sharpness of the citron line of CIS but increases in 

 brightness. It also renders the deep blue line of Ga extremely 

 bright. The green lines of G3 are diminished in brightness. 

 Lime also brings out the phosphorescence of samarium, although 

 by itself, or in the presence of a small quantity of yttrium, 

 samarium scarcely phosphoresces at all. 



In the phosphoroscope the action of lime on yttrium is Fecn to 

 entirely alter the order of visibility of the constituents of yttrium. 

 In a mixture of equal parts yttrium and calcium, the citron G5 

 line is the first to be seen, then comes the Go blue lin-*, then the 

 G3 green line, and finally the CJij red line. .This may, I think, 

 be explained somewhat as follows : — Calcium sulphate has a 

 long residual phosphorescence, whilst yttrium sulphate has a 

 comparatively short residual phosphorescence. Now with 

 yttrium, although the green phosphorescence of G5 lasts longest, 

 it does not last nearly so long as that of calcium sulphite. The 

 long residual vibrations of the calciunr compoimd induce, in a 

 mixture of calcium and yttrium, phosphorescence in those yttric 

 molecules (G5) whose vibrations it can assist, in advance of 

 those (G5) to which it is antagonistic ; the line of GS therefore 

 appears earlier in the phosphoroscope than that of G/3, although 

 were calcium not present the line of G3 would appear first. 



Experiments were now tried with different mixtures of yttria 

 and lime as ignited sulphates, to see where the special influence 

 of lime on G5 ceased. 



The action of barium on yttrium was now tried, 

 ing mixtures (as ignited sulphates) were made : — 



Per Clint. 



974 



Calcium 



Per cent. 

 2i 



Order of appearance in the phosphoroscope. 

 — G3, (/a, G5, and Gt;. The citron line 

 of G5 is only to be seen at a high speed, 

 and is then very faint. 



Order of appearance in the phosphoroscope. 

 — Go, G/3, and GS (citron and blue) to- 

 gether, and lastly Gt) (red). At a very 

 high speed the green line^ of G;8 become 

 far more luminous than any other line. 



Order of appearance. — GS and Go together, 

 then G/3, and lastly Gt). 



Order of appearance. — V>^ and Go simul- 

 taneously, then G/3, and lastly Gt). The 

 residual phosphorescence lasts for 30 

 seconds after the current stops. The 

 light of this residual glow is entirely that 

 of G5. The line of GS comes into view 

 at an interval of O'0O|5 second. At 

 o'ooiyf second the line of Gri is just 

 visible. 



Order of appearance. — GS and Go together, 

 then GS and Gt) together. 



Order of appearance. — GS, Go, G3. 



Order of appearance — G5, Go. The green 

 lines of GS c )uld not be seen in the phos- 

 phoroscope ; they would probably be 

 obliterated by the stronger green of the 

 continuous spectrum given by the calcium. 



05 



99 "5 



In the phosphoroscope the GS line appears 

 earliest, but the blue Go line is the next 

 to be seen, whilst the red line of G») is the 

 latest in appearing. As the percentage 

 of yttrium increases the blue line more 

 and more overtakes the red and increases 

 in brightness. 

 .Spectrum similar to the above. As the 

 percentage of yttrium increases the spec- 

 trum grows brighter. In the phosphoro- 

 scope the earliest line to appear is the 

 GS green, then the Gj) red, and next 

 closely following it the Go blue. 



In the radiant-matter tube all these mixtures 

 give similar spectra. The GS green is a 

 little brighter and the GS citron is a little 

 fainter than in the corresponding mixtures 

 of yttrium and calcium, but the whole of 

 the yttrium lines are seen. In the phos- 

 phoroscope the GS green is the first to 

 appear, then the Gt; red. The GS citron 

 is not visible at any speed. 



Red line of Gt; is nmch brighter ; GS is 

 very faint, and the green of GS is stronger. 

 1 In the phosphoroscope the order of ap- 

 pearance is, — first the line of GS, then 

 the red line of Gtj. 



Phosphoresces with difficulty, of a light 

 blue colour, but turns brick-red in the 

 focus of the pole. Spectrum very faint. 

 Order of appearance to phosphoroscope, 

 — GS first, the others too faint to be teen. 



The next experiments were tried with strontium, to see w'hat 

 modification the addition of this body to yttrium would produce. 

 The foUoiving mixtures ofignited sulphates were experimented 

 with ; — 



In a paper read before the Royal Society, June 18, 1S85. 

 (Phil. Trans., 1885, Part II., p. 716), I describe! the phos- 



