238 C. PIAZZI SMYTH ON NOTE ON SIR DAVID BREWSTER'S LINE Y. 



Though not quite so far to that end of the spectrum as certain two lines of 

 Rubidium, yet being much more constant and more easily procured, these new 

 lines may be useful to other researchers as references for spectrum place in 

 that rather barren region. I give their approximate Wave-number readings 

 therefore here, and have depicted their appearance in the last or " appended " 

 spectrum strip of our table, desiring to remark only, in addition, that the 

 middle line of the three is triple, the distance between its first and second 

 components being rather greater, and between its second and third rather less, 

 than the potassium a * aml 2 pair, whose Wave-number places are 32 988 and 

 33 128, respectively ; while all the three air lines appear fairly sharp, with a 

 narrow slit, and under a dispersion of 12° A to H, combined with a magnifying 

 power on the inspecting telescope of 15. 



Air Line 1, Rel. Intensity = 5, Wave-number place in Brit. Inch = 32 693 

 r Its " a " component, Intens. = 5, W.N.P1. „ = 33 944 



Air Line 2, ) „ "b" „ „ =3, „ „ =34071 



\ ,, c ,, „ =2, ,, ,, =34 157 



Continuous spectrum begins soon after this, and goes on increasing towards the violet. 



Air Line 3, Rel. Intensity = 6, W.N.P1. in Brit. Inch. =35 404 



First Air Line in Dr Watts' Index of Spectra, Intens = 6, W.N. PI. = 38 470 



Note added on May 30, 1884. 



In the course of sundry spectroscopic experiments on vacuum tubes 

 through the winter of 1883-4, and now communicated to Royal Society, 

 Edinburgh, I have had abundant testimony that the first of the lines noted 

 above, viz., at 32 693 Wave-number place, is an oxygen line ; a very remarkable 

 one too, for though like all other "tube," or simple-spark, oxygen lines, it is 

 very faint, — yet it is well-defined, and is further towards the ultra red than any 

 line or band I have yet come across in any of the other gases. 



The triple line which follows I have equally proved to belong to nitrogen. 



But to what gas, air line 3, at 35 404 Wave-number place belongs, I have 

 obtained no indication as yet from vacuum tubes. C. P. S. 



