468 Mr. J. D. Morgnn on Impulsive 



always the most definite. The same experiments were 

 repeated many times at intervals extending over several 

 weeks, and always the same voltage value was found for 

 the first point. The contact-breaker in the primary circuit 

 of the induction-coil was operating at a speed of about four 

 breaks per second, and with the primary current adjusted 

 until sparking at the test gap was just possible, the irregu- 

 larities noticed at different times were not in the spark 

 voltage but in the frequency with which the sparks occurred. 

 The lag at the first point appears to* correspond with what 

 Campbell terms the regular lag, and the lag observed by 

 Peek in his experiments. Proceeding now along any one of 

 the curves, two changes were observed. In the first place, 

 the sparking became more regular until eventually a spark 

 followed each break of the primary circuit, and in the 

 second place the sparking voltage gradually became less 

 regular. But in none of the experiments recorded by the 

 curves w r as the voltage so irregular as to make the drawing 

 of a curve unjustifiable (as is the case with some gaps). 

 These irregularities appear to correspond with Campbell's 

 irregular lag, and are mainly if not entirely due to vari- 

 ations in the ionization of the gap immediately prior to the 

 passage of the spark. Judging from his book {' Dielectric 

 Phenomena in High Voltage Engineering/ iSew York, 

 1915), Peek does not appear to have investigated sparking 

 voltages for a given gap higher than those corresponding to 

 the first point above mentioned, and this accounts in the 

 writer's opinion for the absence (commented on by Camp- 

 bell) of any reference by Peek to irregular sparking voltages. 

 [n considering the above-mentioned irregularities it is not 

 overlooked that they may be due, at least in part, to irregu- 

 larities in the operation of the contact-breaker causing the 

 rate of rise of voltage to vary. Such a condition does 

 undoubtedly account for some irregularity (a condition 

 which would become more accentuated as the primary current 

 is increased), but it does not account for all. It is more 

 probable that the irregularities observed w T ere due mainly 

 to variations in the initial ionization of the gap. As bearings 

 on this point it is necessary to remark that on different days 

 under different atmospheric conditions the same curves could 

 not always be repeated. The clotted line curve in figure 4 

 shows for example one variation which was found. Here 

 the first point was very definite and the same as before, but 

 with increase of primary current the voltage readings became 

 not only rather irregular as before but also quite different. 

 Subsequently the tests were extended to a variety of gaps 



