BELL. — ULTRAVIOLET COMPONENT IN ARTIFICL\L LIGHT. 11 



Q^iartz Mercury Lamp. — Following the examination of the ordi- 

 nary glass Copper Hewitt tube, the next source investigated was the 

 quartz mercury lamp. Two tubes were available, each of the ordi- 

 nary commercial 220 volt type rated at 3.5 amperes. One of these 

 tubes, which is here referred to as the old mercury lamp, was made by 

 the French Cooper-Hewitt Company and, had been already used for 

 experimental purposes for about a year and had seen rather hard 

 service, having often been worked above its rated amperage. The 

 second lamp was entirely new, made in the Cooper-Hewitt factory in 

 this country and was not at any time worked above its rating. The 

 spectrum of the quartz lamp is extremely rich in certain portions of 

 the ultra violet, particularly in rays of wave length less than 300 nix. 

 It is well shown in Spectrum e of Plate 1. The brilliant lines in this 

 spectrum, counting from the violet, have wave lengths as follows: — 



4077.84 

 4046.55 

 3983.96 

 3906.47 

 3663.271 

 3662 .88 

 3654.83 I 

 3650.14 J 

 3341 .48 

 3131.84] 

 3131.56 \ 



3125.67 



3027 .49 

 3025.61 

 3023 .43 I 



302 1.50 J 



The wave lengths here are taken at the value assigned by Stiles ^^ 

 in A. u. It will be observed that a number of the lines are associated 

 in close groups which with small dispersion mass into heavy lines. 

 The relative intensity of the lines, as is well known, shifts consid- 

 erably with the degree of excitation of the tube, so that the relative 

 intensities given by Stiles do not agree with the spectrograms taken 

 from the quartz arc for the same reason that Stiles' arc and spark 

 intensities do not agree. The quartz arc spectrum resembles Stiles' 

 arc spectrum much more closely than it does the spark spectrum. 



^^ Astrophysical Journ., Vol. XXX, p. 48. 



