Steam developes Positive Electricity. 99 



with the internal surface of the glass bell, on the superficial 

 contents of which the quantity of electricity developed greatly 

 depends. On a larger scale, as in a steam-engine, the air in 

 which the cloud originates has the same function as the glass 

 surface. In thundei- storms the currents of air rushing towards 

 the centre of the nascent cloud, produce the pecuhar sudden 

 condensation and separation of water-gas similar to the pencil 

 of steam issuing with the fluttering noise already mentioned 

 from the jet of the boiler. 



I must here particularly impress on the reader, that as the 

 pencil of steam developes electricity only under certain cir- 

 cumstances, that is when steam is mixed with minutely-divided 

 water before its expansion, so the thunder-cloud must like- 

 wise be in a similar state in respect to its water-gas and mi- 

 nutely-divided water, quite different to the state of a rainy 

 atmosphere, where the condensation of the watei'y vapour into 

 the shape cf clouds commences only in the highest and 

 coldest regions, uniformly and gradually, and where during 

 their descent at certain intervals, from the highest to the lowest 

 regions, the atmosphere begins gradually and uniformly to 

 discharge moisture until the hygrometer indicates the point 

 of saturation at which the formation of drops commences. 



The electricity developed by evaporation, 8cc. could never 

 manifest itself in a metallic boiler, and is under the most fa- 

 vourable circumstances so feeble, that its existence was long 

 denied by the most eminent philosophers, until Dr. Harris 

 succeeded unequivocally in demonstrating its presence. This 

 electricity is likewise much influenced by chemical actions 

 ensuing at the same time, as M. Pouillet has distinctly proved, 

 which was not the case in my experiments. 



With the positive electricity obtained from a jet of con- 

 densed steam, negative electricity is at the same time deve- 

 loped in the boiler and water, and as far as I was able to 

 judge, of the same intensity. Negative electricity derived 

 from a locomotive engine must necessarily be affected by the 

 chemical process of combustion going on at the same time 

 on a very extensive scale, as well as from various other causes, 

 such as imperfect insulation, points, and sharp edges, and I 

 was not able to detect in my small boiler any traces of nega- 

 tive electricity, if at the same time positive electricity did not 

 appear in the glass bell. 



H2 



