William Sturgeon. 279 



and afterwards plunging them into mercury. He showed 

 that plates prepared in this way do not effervesce in dilute 

 sulphuric acid, as the unprepared plates do, and, in conse- 

 quence, require to be much less frequently renewed than 

 the latter ; whilst, at the same time, the electric current 

 produced is much more intense and constant. It is a 

 remarkable fact, that no further improvement has been 

 effected in the preparation of the positive plates of the 

 galvanic apparatus, and that Mr. Sturgeon's amalgamated 

 zinc plates are, at the present day, employed in every form 

 of improved battery, whether patented or not. 



* In our chronological arrangement of Mr. Sturgeon's 

 discoveries, we may next note a highly valuable paper on 

 the Thermo- Magnetism of Homogeneous Bodies^ a work the 

 merit of which can only be duly appreciated by those who 

 are acquainted with the extreme minuteness of the currents 

 of which it was the object to discover the existence and 

 direction. By a happy combination of industry and sa- 

 gacity, our author succeeded in proving that electric cur- 

 rents can be developed in any individual mass of pure 

 metal by a mere disturbance of temperature at some 

 particular point, and that the direction of those currents 

 is determined by the position of the point of greatest heat 

 and the crystalline structure of the metal — a fact of the 

 highest importance, and which, along with others developed 

 by him about the same time, paved the way to Dr. Faraday's 

 celebrated discovery of magnetic-electricity. 



'In 1836 Mr. Sturgeon communicated a paper to the 

 Royal Society, which contains the description of a perfectly 

 original magnetic electrical machine^ in which a most 



' This instrument is the precursor of the variety of modern dynamo-electric 

 machines employed for the electric light, electro-plating, telegraphing, &c. 



