Nolan and Enright — Electrification Produced hj Breaking up Water, 1 1 



impurities in modifying the electrical conditions at the surface-layer is probably 

 connected with their effect in reducing the degree of pulverization produced at a 

 given spraying pressure. The impure water can, to a certain extent, readjust its 

 surface-tension under applied stresses; the pure water is, as it were, more 

 " brittle." 



Our measurements show that the quantity of electricity associated with the 

 formation of 1 sq. cm. of new water surface is about 0'02 e.s. units. 



Results considered in connexion with Simpson's " hreaking-drop " theory. 



In this connexion the outstanding feature of these experiments is the importance 

 of purity of the water when the degree of breaking up is small. Our purest sample 

 of water had a specific conductivity of 2'4 x 10"" ohm'', which does not indicate a very 

 high degree of purity. This water stood for days in an earthenware vessel in contact 

 with air, and, of course, was also in contact with glass vessels. The nature of the 

 contamination that affects the activity of the water from the electrical point of 

 view we do not know. This is a point we hope to investigate subsequently. But 

 it is not unreasonable to suppose that a rain-drop, formed in the well-filtered air of 

 a thundercloud, is much purer than our purest sample. Hence, for moderate degrees 

 of breaking up, we would expect the thunder-rain to acquire bigger charges than 

 those observed by us. But even for the same degree of purity it can be seen that 

 the charges observed on thunderstorm-rain can easily be reached. If a drop of 

 radius r breaks up into 27 equal drops,' the change in surface per c.c. is 6/r. Taking a 

 drop of diameter 4 mm., the change in surface per c.c. will be 30 sq. cm. Eeference 

 to fig. 4 shows that this would produce, in our purest sample, a charge somewhat 

 greater than 0"2 e.s. units per c.c. We see, therefore, that for the purer water of 

 the thunderstorm we need not demand any high degree of breaking up or any 

 very sustained repetition of the process in order to produce the charges observed 

 on thunder-rain. There is another process at work which tends to concentrate 

 the charge. It is recognized that evaporation from the falling rain-drops in a 

 thunderstorm is very rapid. Evaporation no doubt also plays a part in increasing 

 the magnitude of the charge per c.c. on ordinary rain. We consider, therefore, 

 that if a moderate degree of purity be assumed for rain-drops in the upper 

 atmosphere, the theory put forward by Simpson is fully competent to account for 

 the observed electrical phenomena of thunderstorms. It also explains the sign and 

 magnitude of the charge on the greater part of ordinary rain. 



' See Hochschwender's photograph, fig. 6. Lenard, loc. cit. 



