On t/tr tfjwfrn.tii <>/'//>< more. Volatile Gas** of Air. 473 



st of Approximate Wavelengths of the L'n>/.-; /7>-/V//r a,,// Ultra-violet, 



flic \r</<ifirr Poll'. 



The rays of hydrogen and helium, and those attributed to neon by 

 other ol (.servers, are indicated by the chemical symbols of those sub- 

 stances : 



A " b " prefixed to the number expressing the wave-length indicates 

 that the ray is emitted by gas from the Bath spring as well as by that 

 obtained from the atmosphere. 



A " c " similarly prefixed indicates that the ray has been observed 

 to be emitted from the capillary part of the tube as well as from about 

 the negative pole. 



A " w " indicates a weak line ; " s " a strong one ; " d " a diffuse 

 one ; " vw " a very weak ; and t; vs " a very strong one. 



