1838] WRITINGS OF JOSEPH HENRY, 145 



about a year since. No published account of these experi- 

 ments has yet reached this country, but it appears that Pro- 

 fessor Ettingshausen had been led to suspect the develop- 

 ment of a current in the metal of the keeper of the magneto- 

 electric machine, which diminished the effect of the current 

 in the coil about the keeper, and hence to separate the coil 

 from the keeper by a ring of wood of some thickness, and 

 afterwards, to prevent entirely the circulation of currents in 

 the keeper, by dividing it into segments, and separating them 

 by a non-conducting material. I am not aware of the result 

 of this last device, nor whether the mechanical difficulties in 

 its execution were fully overcome. It gives me pleasure to 

 learn that the improvements, which I have merely suggested 

 as deductions from the principles of the interference of in- 

 duced currents (76), should be in accordance with the experi- 

 mental conclusions of the above named philosopher.* 



*[Re-printed in Silliman's American Journal of Science, March, 1840, 

 vol. xxxviii, pp. 209-243.] 



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