TRANSACTIONS 



ROYAL IRISH ACADEMY. 



J.— On Galvanometric Deflections producible by Attrition and Contact of Metals 

 under certain circumstances. By Michael Donovan, Esq., M. B. T.A. 



Head Jaouary 8, 22, and February 12, 1849. 



It is known that under certain circumstances of temperature some metals 

 -when connected with a galvanometer, and brought into contact with each other, 

 produce a deflection of the magnetic needle, which will appear to be reversed 

 when, instead of contact, attrition is employed. 



Such facts have given rise to much difference of opinion, and, as I conceive, 

 to much misapprehension both of the phenomena and their cause. Professor 

 Erman of Berlin, who had devoted his attention to the subject, thus sums up 

 the opinions current upon it: — " Some observers, who appeal to the authority of 

 Mr. Emmet, express what they consider to be the law of this action, by saying 

 that thermo-electricity of contact is changed invariably into the opposite state by 

 the friction of the metallic factors. Others, on the contrary, deny in toto the 

 influence of friction on thermo-electric phenomena. Thus it was recently 

 adverted to in a scientific journal as a highly paradoxical fact that, in a 

 given case, the friction had caused a change of sign in the thermo-electric decli- 

 nation produced by the contact of two heterogeneous metals, but, at the same 

 time, this ' unheard-of fact, as it was called, was explained by supposing, gra- 

 tuitously, that the friction had been effected whilst keeping the metal to be 



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