INTENSITY RELATIONS IN THE SPECTRUM OF HELIUM. 173 



that the addition of a trace of Hydrogen affects both the Diffuse and the Sharp series 

 to a comparable extent, whilst the inverse effect produced, by a larger quantity of 

 the lighter gas, affects the Diffuse series to a much greater extent than the Sharp 

 series. 



Finally, we may refer again to the qualitative results, which show that the seat of 

 maximum emission is widely different for lines of Helium, Hydrogen and Mercury, 

 and can be very strikingly seen in spite of the heterogeneous nature of the excitation 

 in our tubes. An explanation of the apparent distribution of the elements in celestial 

 bodies upon such a basis might be worthy of consideration, but the experimental 

 evidence seems hardly sufficient to justify such an extrapolation. 



