288 Crooker — Influence of a Series Spark 



6,000 RPM. The lenses are set about four inches from 

 the center of the disc so that it is possible to get a linear 

 speed of approximately 100 feet per second across the 

 face of the photographic plate. 



By this method it is possible to analyze the spark and 

 to determine whether it is of an oscillatory or unidirec- 

 tional character. An oscillatory spark will give an 

 irregular band of light across the plate (see fig. 5a), while 

 a unidirectional spark leaves only a sharp line (see dines 

 in fig 5b). 



For rough determinations it is easy to observe the 

 image of the spark on the ground glass plate of the cam- 

 era and quickly find if the spark is oscillatory or 

 not. If it is oscillatory one can observe the approxi- 

 mate frequency and duration of the spark. For more 

 accurate determinations photographs must be made on 

 sensitive plates and observations and measurements 

 made from them. 



Several observations were made with this method for 

 various spark lengths and speed of lenses using both air 

 and hydrogen in the corona tube. In the first experiment 

 corona was produced in air at a pressure of 500 mm. by a 

 potential of 14,000 volts. The spark gap was about 1-5 

 mm. in length and the lenses were driven at a speed of 

 2,000 RPM. A photograph was taken but the individual 

 sparks showed no trace of being oscillatory. 



To spread the individual spark images out the lenses 

 were driven at a higher speed of 6,000 RPM. and the 

 spark gap set at 1-19 mm. This arrangement allowed a 

 passage of about 2,500 sparks per second and a speed of 

 about 100 feet per second across the plate. The photo- 

 graph, fig. 5b, clearly showed that the sparks were not of 

 aii oscillatory character but unidirectional, only a sharp 

 line was recorded as each spark passed and their dura- 

 tion was less than 1/100,000 second. Moreover, each 

 spark was a little brighter at the negative electrode, 

 showing that they all passed in the same direction and 

 were of the same character. ^ 



With hydrogen in the tube at a pressure of 744 mm. 

 and a potential of 9,400 volts photographs were taken 

 when the spark gap was 0-75 mm. and 0-3 mm. in length. 

 For the 0-75 mm. gap the frequencv of the sparks was 

 about ten per second producing a large number of silvery 

 streamers in the corona tube. When the gap was reduced 



