ON THE THERMAL DEVELOPMENT OF THE SPARK 

 SPECTRUM OF CARBON. 



By Henry Crew and John C. Baker. 



Presented by Charles R. Cross, October 8, 1902. Received Octobers, 1902. 



During the course of some experiments which Professor Basquin was 

 making on the production of arc and spark spectra from the same elec- 

 trodes, it was observed by one of us, standing at the eyepiece of his spec- 

 troscope, that the lines of the spark spectrum made their appearance 

 gradually, and not suddenly, beginning at the instant at which the direct 

 current feeding the arc was cut off and the high-voltage current producing 

 the spark was switched on. 



It was evident at once that the appearance of these lines in deliberate 

 succession was due, primarily at least, to the gradual cooling of the elec- 

 trodes and of the region between them. But we were uncertain whether, 

 after all, the effect was not merely a physiological one, the lines first 

 observed being the stronger lines, and those observed later being the 

 weaker lines. We accordingly set about making a series of photographs 

 which should show the spark spectrum at each successive instant begin- 

 ning at the time at which the arc current is interrupted. 



At first our attempt was to employ metallic spark-electrodes for the 

 spectrum and to use the carbon arc to heat the spark gap. And in order 

 to retard the development of 

 the spark as much as possible, 

 the carbon electrodes were en- 

 closed between two saucer- 

 shaped clay scorifiers as shown 

 in Figure 1. The terminals of 

 the spark circuit were intro- 

 duced into this cell at right 

 angles to those of the arc. 

 Various other forms of cells, 

 hollowed limes from the stere- 

 opticon, clay pipes, fire brick, Figure 1. 



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