Mr. W. G. Armstrong on the Electricity of Effluent Steam. 453 



propagated under different pressures, and from water of va- 

 rious descriptions ; and by insulating myself and holding a 

 conducting-rod in the steam discharged from the safety- 

 valves, I succeeded in every instance in obtaining electrical 

 sparks, which varied in the different cases from about one- 

 fourth to about half an inch in length. 



In company with Mr. Robert Nicholson, the engineer of 

 the Newcastle and North Shields railway, I next tried the 

 boilers of the locomotive engines used on that railway, and 

 finding electricity in great abundance in the ejected steam 

 from these boilers, I determined, with Mr. Nicholson's per- 

 mission and assistance, to institute a set of experiments upon 

 one of them, with a view to a fuller investigation of the sub- 

 ject. 



I shall now briefly describe such of these experiments as 

 have been the most marked in their results, and shall divide 

 them into two classes, first taking those which were chiefly in- 

 tended to exhibit the extent to which electricity existed in 

 the issuing steam, and then proceeding with the experiments 

 which were undertaken to ascertain the cause of the electric 

 development. Nearly all the experiments were made at 

 night, under cover of the engine-shed, and the atmosphere 

 was generally humid ; but when it happened to be otherwise, 

 the quantity of electricity derived from the jet was greatly 

 increased. 



Upon trying the steam in the first instance by the method 

 adopted in the previous cases, that is to say, by standing on 

 an insulated stool and holding with one hand a light iron 

 rod immediately above the safety-valve, while the steam was 

 freely escaping, and then advancing the other hand towards 

 any conducting body, sparks of about an inch in length were 

 obtained : but it was soon observed, that by elevating the rod 

 in the steam the electricity was gradually increased, and that 

 the maximum effect was not attained until the end of the 

 rod was raised five or six feet above the valve, at which point 

 the length of the sparks occasionally reached two inches. 

 Small sparks were even obtained when the rod was wholly re- 

 moved from the steam and held in the atmosphere at the 

 distance of two or three feet from the jet, and the electricity 

 thus drawn from the air was positive, like that of the steam. 

 When the rod was extended into the cloud of vapour which 

 accumulated in the upper part of the shed, electricity was 

 drawn down as by a lightning-conductor from a thunder- 

 cloud. I endeavoured to ascertain whether any precipitation 

 of moisture, analogous to the formation of rain, accompanied 



