A FLASH OF LIGHTNING 79 



Here we have a representation of the outflow into tlie cloud which 

 has less than its normal charge. The flash here difl^upcs into the cloud, 

 and the outer portions of the flash might well be called sheet lightning. 

 The conditions which would bring about the brief dash of large rain- 

 drops do not appear to exist at this end of the lightning flash. 



Figs. 3 and 4 are similar to Figs. 1 and 2, the discharge being some- 

 what more violent, or greater in quantity'. In Fig. 3, it may be seen 

 that the inflow in some eases begins at isolated points, and progresses 

 inwardly towards inflow lines which are elongating in a direction 

 opposite to that in which the flow is taking place. 



If these discharge figures are to be described in the language of the 

 two-fluid theory, Figs. 1 and 3 must be called an outward positive dis- 

 charge. Figs. 2 and 4 must be called an outward negative discharge. 

 We must say that the outward negative discharge shown in Figs. 2 and 

 4 came from the cloud represented in Figs. 1 and 3, and that the out- 

 ward positive discharge, shown in Figs. 1 and 3, came from the cloud 

 represented in Figs. 2 and 4. 



Such an explanation seems so essentially absurd in the presence of 

 these photographic plates, that it will not be urged. 



In conclusion, however, a confession must be made. The lightning 

 discharge here described was artificially produced. A plate-glass 

 machine, with metal conductors terminating in pin-heads took tlie 

 place of the long flash of lightning. The pin-heads rested upon the 

 centers of the two photographic films, the plates resting on large sheets 

 of glass. There were small spark-gaps of about half an inch in each 

 line, at the machine terminals. A single spark across these gaps pro- 

 duced a glow over the films around the pin-heads. In order to bring 

 some of the discharge lines down into close proximity to the films, so 

 that they would be sharply defined, copper plates were placed under 

 each photographic plate below the sheet of glass. These copper plates 

 were grounded or, what produces the same result, they were connected 

 with each other. Xo trace of the discharge can be detected until the 

 photographic plate is developed. With this confession, and with an 

 apology for having misled the reader, the question may be asked, can 

 any one look at Figs. 1 and 3 and believe that they are produced by an 

 outward discharge of positive electricity? These plates tell their own 

 story. They represent an inflow of negative corpuscles, along drainage 

 channels. 



Some of the lines are not sharply defined. They are too far above 

 the film. They all present a shadowy appearance, if the condenser 

 action of the copper plates is eliminated. 



