56 Mr Meikle on the Electricity, Sfc. of Steam. 



found the electricity so evolved to be positive ; but it is curious 

 to observe how inaccurately in other respects they have ex_ 

 pressed themselves regarding the phenomenon, calling it " the 

 rapid production of electricity which appears to accompany 

 the generation of steam," " the evolution of electricity by va- 

 porization," and " the evolution of electricity during the con- 

 version of water into vapour ;" whereas the electricity was 

 evidently evolved by a process just the Aery reverse, viz. by 

 the sudden change of transparent steam into water ; for a cloud 

 Just consists of minute drops of water. The novelty in this 

 case seems, after all, to consist chiefly in the intensity of the 

 electricity; for the evolution of positive electricity, when trans- 

 parent aqueous vapour suddenly assumes the form of a cloud, 

 had been so often observed before as to leave little doubt that 

 it will be found to hold universally when once adequate means 

 have been devised for detecting it ; and conversely, that steam, 

 instead of evolving electricity at its formation, must then ab- 

 sorb it as a necessary and constituent ingredient. Dr Faraday 

 thinks the case observed at the Cramlington colliery " brings 

 us much nearer to the electrical phenomena of volcanos, wa- 

 ter-spouts, and thunder-storms than before ;" but not nearer, 

 I presume, than Mr Espy's new theory (which, as noticed in 

 the last number of this Journal, I had published near a dozen 

 years ago) does ; because it just refers these phenomena to 

 the evolution of electricity by the sudden condensation of 

 aqueous vapour. 



Water requires a higher temperature to make it boil in a 

 glass vessel than in one of metal, and in the former, too, it 

 boils more violently, probably because the glass, being a bad 

 conductor, cannot so well supply the electricity for the forma- 

 tion of steam. When, therefore, the lower part of a steam- 

 boiler becomes incrusted with a bad conductor of electricity, 

 the temperature may be raised till the water boil so violently, 

 especially under the feeble pressure of the imperfectly formed 

 steam, as to reach the upper parts of the boiler, which, hav- 

 ing little or no incrustation, may then supply the electricity 

 so suddenly to the water and steam already at a high tempe- 

 rature, as to increase the force of the steam to a degree which 

 occasions a violent explosion before there is time for the safety- 



