1892.] to produce, a Spark in Air at different Pressures. 1 11 



. 6. 



screw caliper might be very different from that due to the weight of 

 the supported plate, especially in those cases in which several thick- 

 nesses of mica or ebonite were used. The essential point of this part 

 of the investigation, however, was not the accurate determination of 

 spark-length, but the direct comparison of discharge across two 

 spark-gaps known to be of very different length. 



The following table, similar to that given on p. 107, gives corre- 

 sponding values for minimum potential difference, spark-length, arid 

 pressure, as deduced from the curves of fig. 6 : 



