OP ARTS AND SCIENCES. 295 



our apparatus, for it could not be produced at will by changing the 

 position of the source of light. Moreover, when the arc light was 

 placed in the same position that the spark occupied, no displacement 

 could be observed in photographs taken by the aid of tbe arc. We 

 were forced to conclude that through the range of temperature af- 

 forded by the electric arc and the electric spark the wave-lengths of 

 the metallic lines were constant. The displacement we observed was 

 therefore referred to a jarring of the apparatus due to the noise of the 

 electric spark. When the camera was at a considerable distance from 

 the slit of the spectroscope, the displacement was diminished, and 

 sometimes entirely disappeared. The entire apparatus was very solid, 

 and the camera was clamped to a massive girder. It was difficult, 

 therefore, to believe that the displacement could arise from the noise 

 of the spark. We believe, however, that it can be ascribed to this 

 cause, and that the wave-lengths of metallic lines produced by burn- 

 ing metals in the electric arc or by vaporization in the electric spark 

 are to one hundredth of a wave-length the same as those of the corre- 

 sponding lines in the sun. 



Results. 



In the following table we have adopted the same symbols and 

 letters to designate the character of the lines which the Committee of 

 the British Association have employed. Column 1 refers to the in- 

 tensity on a scale of 10. Column 2 gives our measures of the wave- 

 lengths of the copper lines in the ultraviolet, from wave-length 2369.9 

 to 1944.1. Column 3 contains the measures of these lines by Hartley 

 and Adeney. Column 4 are the corrections to be applied to Hart- 

 ley and Adeney's results. Column 5 contains measurements by Live- 

 ing and Dewar. Column 6, corrections to be applied to their results. 

 Column 7 gives the symbols adopted by the Committee of the British 

 Association, which serve to describe the character of the line. 



