Jan. 9, 1879] 



NATURE 



229 



Frankland and myself, in 1S69, found that it only made 

 its appearance when a high tension was employed. We 

 have seen that it was absent from among the hydrogen 

 lines during the eclipse of 1875. 



I have now to strengthen this evidence by the remark 

 that it is always the shortest line of hydrogen in the 

 chromosphere. 



I now pass to another line of evidence. 



I submit to the Society a photograph of the spectrum 

 of indium, in which, as already recorded by Thalen, the 

 strongest line is one of the lines of hydrogen {fi), the 

 other line of hydrogen (near G) being absent. I have 

 observed the C line in the spark produced by the pas- 

 sage of an induced current betv/een indium poles in dry 

 air. 



As I am aware how almost impossible it is to render 

 air perfectly dry, I made the following differential experi- 

 ment. A glass tube with two platinum poles about half 

 an inch apart was employed. Through this tube a slow 

 current of air was driven after passing through a (J-tube 

 one foot high, containing calcic chloride, and then through 

 sulphuric acid in a Wolft's bottle. The spectrum of the 

 spark passing between the platinum electrodes was then 

 observed, a coil with five Grove cells and a medium- 

 sized jar being employed. Careful notes were made of 

 the brilliancy and thickness of the hydrogen lines as 

 compared with those of air. This done, a piece of 

 metallic indium, which was placed loose in the tube, was 

 shaken so that one part of it rested against the base of 

 one of the poles, and one of its ends at a distance of 

 a little less than half an inch from the base of the 

 other pole. The spark then passed between the indium 

 and the platinum. The red and blue lines of hydrogen 

 were then observed both by my friend Mr. G. W. 

 Hemming, Q.C., and myself. Their brilliancy was most 

 markedly increased. This immistakable indication of 

 the presence of hydrogen, or rather of that form of 

 hydrogen which gives us the h line alone associated into 

 that form which gives us the blue and red lines, showed us 

 that in the photograph we were not dealing with a physical 

 coincidence, but that in the arc this special form of hydro- 

 gen had really been present ; that it had come from the 

 indium, and that it had registered itself on the photo- 

 graphic plate, although ordinary hydrogen persistently 

 refuses to do so. Although I was satisfied from former 

 experiments that occluded hydrogen behaves in this 

 respect like ordinary hydrogen, I begged my friend Mr, 

 W. C. Roberts, F.R.S., chemist to the Mint, to charge a 

 piece of palladium with hydrogen for me. This he at 

 once did, and I take this present opportunity to express 

 my obligation to him. I exhibit to the Society a photo- 

 graph of this palladium and of indium side by side. It 

 will be seen that one form of hydrogen in indium has 

 distincdy recorded itself on the plate, while that in pal- 

 ladium has not left a trace. I should add that the 

 palladium was kept in a sealed tube till the moment of 

 making the experiment, and that special precautions were 

 taken to prevent the two pieces between which the arc 

 was taken becoming unduly heated. 



To sum up, then, the facts with regard to hydrogen ; 

 we have h differentiated from the other lines by its appear- 

 ance alone in indium ; by its absence during the eclipse 

 of 1875, when the other lines were photographed ; by its 

 existence as a short line only in the chromosphere of the 

 sun, and by the fact that in the experiments of 1869 a very 

 high temperature was needed to cause it to make its 

 appearance. 



With regard to the isolation of the F line I have 

 already referred to other experiments in 1869, in 

 which Dr. Frankland and myself got it alone.^ I ex- 

 hibit to the Society a globe containing hydrogen which 

 gives us the F line without either the red or the blue 

 one. 



' See also Plucker, Phil. Trans., 1865, part i, p. 21. 



The accompanying drawing shows how these lines are 

 integrated in the spectrum of the sun. 



Fig. 6. 



I have Other evidence which, if confirmed, leads to the 

 conclusion that the substance which gives us the non- 

 reversed line in the chromosphere and the line at 1474 

 of Kirchhoffs scale, termed the coronal line, are really 

 other forms of hydrogen. One of these is possibly more 

 simple than that which gives us h alone, the other more 

 complex than that which gives us F alone. The evidence 

 on this point is of such extreme importance to solar 

 physics, and throws so much light on star structure gene- 

 rally, that I am now engaged in discussing it and shall 

 therefore reserve it for a special commimication. 



In the meantime I content myself by giving a diagram 

 in which I have arranged the various groupings of 

 hydrogen as they appear to exist, from the regions of 

 highest to those of_^lowest temperature in our central 

 luminary. 



Fig. 7. 



Summation of the above Series of Facts 



I submit that the facts above recorded are easily 

 grouped together, and a perfect continuity of phenomena 

 established on the hypothesis of successive dissociations 

 analogous to those observed in the cases of undoubted 

 compounds. 



The other Branches of the Inquiry 

 When we pass to the other possible evolutionary pro- 

 cesses to which I have before referred, and which 

 I hope to discuss on a future occasion, the inquirj' 

 becomes much more complicated by the extreme dif- 

 ficulty of obtaining pure specimens to work with, although 

 I should remark that in the working hypothesis now under 

 discussion the cause of the constant occurrence of the 

 same substance as an impurity in the same connection is 

 not far to seek. I take this opportunity of expressing 

 my obligations to many friends who have put them- 

 selves to great trouble in obtaining specimens of pure 

 chemicals for me during the whole continuance of my 

 researches. Among these I must mention Dr. Russell, 

 who has given me many specimens prepared by the 

 lamented Matthiessen, as weU as some of cobalt and 

 nickel prepared by himself ; Prof. Roscoe, who has sup- 

 plied me with vanadium and caesium 'alum ; J^Ir. Crookes, 

 who has always responded to my call for thaUiimi ; Mr. 

 Roberts, chemist to the Mint, who has supplied me with 

 portions of the gold and silver trial plates and some 

 pieces of palladium ; Dr. Hugo Miiller, who has.fumished 

 me a large supply of electrolitically-deposited copper; 

 Mr. Holtzman, who has provided, mej with cerium, 

 lanthanum, and did>Tnium prepared by himself ; Mr. 

 George ^Matthey, of the well-known metallurgical firm of 

 Johnson and Matthey, who has provided me withrnag- 

 nesium and aluminium of mar^'ellous purity ; while to 



