68 Prof. J. Norman Lockyer. [Apr. 25, 



same wave-length as D 3 , which I discovered in 1868. This line 

 Dr. Frankland and myself shortly afterwards suggested might be a 

 line of hydrogen, not visible under laboratory conditions ; but solar 

 work subsequently showed that this view was untenable, although 

 the gas which produced it was certainly associated with hydrogen. 



Subsequently, other chromospheric lines were found to vary with 

 the yellow line, and the hypothetical gas which gave rise to them 

 was provisionally named ''helium," to differentiate it from hydrogen. 



It was therefore of great interest to me to learn whether the new 

 gas was veritably that which was responsible for the solar phenomena 

 in question, and I am anxious to express my best thanks to Professor 

 Ramsay for sending the tube to enable me to form an opinion on this 

 matter. Unfortunately, it had been used before I received it, and 

 the glass was so blackened that the light was invisible in a spectro- 

 scope of sufficient dispersion to decide the question. 



On March 29th therefore, as Professor Ramsay was absent from 

 England, in order not to lose time, I determined to see whether the 

 gas which had been obtained by chemical processes would not come 

 over by heating in vacuo, after the manner described by me to the 

 Society in 1879,* and Mr. L. Fletcher was kind enough to give me 

 some particles of uraninite (broggerite) to enable me to make the 

 experiment. 



This I did on March 30th, and it succeeded; the gas giving the 

 yellow line came over, associated with hydrogen, in good quantity. 



I have since obtained photographs of the spectrum of the gas, both 

 in vacuum tubes while the Sprengel pump has been going, and at 

 atmospheric pressure over mercury. To-day I limit myself to 

 exhibiting two of these photographs. 



One of the photographs exhibits a series of spectra taken during 

 the action of the pump. The two lower spectra indicate the intro- 

 duction of air by a leak after the capillary had cracked near one of 

 the platinums, giving us on the same plate the banded and line 

 spectrum of air. These prove that there was no air present in the 

 tube when the fourth spectrum was taken. This photograph has not 

 yet been finally reduced, but a preliminary examination has indicated 

 that most of the lines are due to the structure spectrum of hydrogen, 

 but not all of them. 



Among the lines which cannot be referred to this origin are two 

 respectively near \4471 and A, 4302, which have been observed in the 

 chromosphere, 4471 being as important as D 3 itself, from the theo- 

 retical point of view, to students of Solar Physics. 



Whilst spectrum No 4 was being photographed with the capillary 

 tube end-on-wise, eye observations were made in another spectroscope 

 directed sideways at it. I give from the Laboratory Note Book the 

 * ' Eoy. Soc. Free.,' rol. 29, p. 266. 



