Physiology. — “On Spray-Electricity and Waterfall- Electricity’. 
By Prof. H. ZWAARDEMAKER and Dr. F. Hogewinp. 
(Communicated in the meeting of October 25, 1919). 
The generation of Spray-electricity and that of Waterfall-electricity 
are no doubt cognate processes; still they are by no means identical. 
It may perhaps be useful, therefore, that we should here enlarge 
upon their congruency and their difference. 
Spray-electricity is generated when the air causes waterdrops to 
break up and diffuse; waterfall-electricity is evolved when existing 
waterdrops strike against a boundary plane of air-liquid or air-solid 
substance. This induces electrification of the spray-nebula at the very 
spot where the cloud arises, whereas the electrical charge of the 
waterfall does not take its beginning before the water reaches the 
bottom. In either case small and large drops are formed with opposite 
charges. Both with spray-electricity and with waterfall-electricity the 
surrounding air is laden to a large distance with those diminutive 
droplets, driven off in all directions. 
With spraying the large drops follow their primitive course till 
they strike on some impediment or other. These drops have become 
electrified long before they encounter this impediment. In the case 
of waterfall-electricity, however, large drops as well as small ones 
form at the very moment when the electric charge begins, i.e. the 
moment when the jet collides with the impediment. 
In either case the conditions of 
“pressure” 
and ‘‘temperature”’ 
largely reinforce the electrical effect. An overpressure of two atmos- 
pheres yields notably more electricity than one atmosphere. To obtain 
a considerable reinforcement of spray-electricity it is only necessary 
to store up the nebula in a space, whose temperature is 10° higher. 
Likewise waterfall-electricity will be considerably increased by heat- 
ing the reservoir from which the waterfall proceeds. The presence 
of an electric field will augment either in a marked degree. 
