6 Mr. Henry Wilde on Helium and 



An induction-coil giving a io-inch spark in air was 

 used in the experiments, and the density of the spark was 

 increased by means of a Leyden jar. The observations 

 were made with the same direct-vision spectroscope of five 

 prisms as was used in my research on the spectrum of 

 thallium. 



The minerals, in coarse powder, from which the gases 

 are to be distilled, are fed into the cylinder through the 

 end into which the tube is screwed, and the joint is after- 

 wards made good by means of a washer of asbestos. 



Dr. Burghardt, Lecturer in Mineralogy at the Owens 

 College, kindly placed at my disposal some heavy zirco- 

 niferous sand, containing uranium, which is found in large 

 deposits on the coast of Brazil. This sand is an abundant 

 source of helium, and, judging from the brightness of the 

 spectroscopic reaction, is not much inferior to cleveite. 



Fourteen grammes of the sand were fed into the cylinder, 

 which, after being exhausted of air, was heated up by the 

 Bunsen flame. As the heat of the cylinder approaches 

 visible redness, the double sodium line and the C hydrogen 

 line make their appearance, and when the pressure in the 

 receiver increases to six inches of mercury, the yellow line 

 and the violet line 4472 of helium become visible. As the 

 heat and pressure increase, the lines of hydrogen and 

 helium widen out, till at a pressure of 15 to 26 inches the 

 helium and sodium lines are nearly of equal width, and 

 appear as single lines in the spectrum. 



This experiment shows that, within certain limits, the 

 distance between the components of D 3 is not to be taken as 

 the criterion of the identity of chromospheric and terrestrial 

 helium. 



As solar temperatures are much too high for the forma- 

 tion of chemical compounds, the coincidence of the 

 characteristic lines of chromospheric and terrestrial helium 

 clearly establishes the elementary nature of the gas or 



