70 MR. J. P. JOULE ON THE LIFE AND WRITINGS 



found that on heating one part of a bar to a full red heat, 

 the remainder acted just as if the heated portion had been 

 removed altogether. 



Mr. Sturgeon had shown, in his " Experimental Researches 

 in Electro- Magnetism and Galvanism," published in 1830, 

 that when two similar plates of iron are placed, one in each 

 of two strong solutions of nitric acid of different degrees of 

 strength, having a bladder partition between them, they form 

 an active voltaic pair : a battery of ten such pairs enabled him 

 to decompose water and to ignite metals. At the same time 

 he showed the high rank held by iron as an electro-negative 

 element, when associated with amalgamated zinc. In 1836 

 Daniell observed that iron is sometimes more efficient than 

 platinum, in association with amalgamated zinc; and about the 

 same time Roberts and Fyfe recommended the employment of 

 iron in the construction of voltaic batteries. In 1839 Mr. 

 Sturgeon constructed a battery, consisting of twelve iron gas 

 tubes, furnished with strips of amalgamated zinc, which proved 

 very efficient. Afterwards, in 1840, he fitted up ten cylin- 

 drical jars of cast iron, each eight inches high and three inches 

 and a-half in diameter, with the same number of amalgamated 

 zinc cylinders of about two inches diameter. Although the 

 electro-motive force of an iron zinc pair is only about one-half 

 that of a Daniell's cell, Mr. Sturgeon's cast iron battery may 

 be advantageously employed in many cases, owing to its great 

 simplicity and cheapness. 



In an experimental investigation of the " Magnetic 

 Characters of Simple Metals, Metallic Alloys, and Salts," 

 published in the seventh volume of the Transactions of this 

 Society, Mr. Sturgeon showed that several metallic alloys 

 became endued with magnetic properties, although their con- 

 stituents separately showed no such action. On the other 

 hand, nickel and iron became almost entirely inert to magnetic 

 action when combined with other metals. An alloy of iron 



