ON ELECTRO-DYNAMIC INDUCTION. 337 



lead to some new and important developments. Indeed every part of 

 the subject of electro-dynamic induction appears to open a field for dis- 

 covery, which experimental industry cannot fail to cultivate with im- 

 mediate success. 



NOTE. 



On the evening of the meeting at which my investigations were 

 presented to the Society, my friend, Dr Bache of the Girard College, 

 gave an account of the investigations of Professor Ettingshausen of Vi- 

 enna, in reference to the improvement of the magneto-electric machine, 

 some 'of the results of which he had witnessed at the University of 

 Vienna about a year since. No published account of these experiments 

 has yet reached this country, but it appears that Professor Etting- 

 shausen had been led to suspect the development 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 over- 

 come. It gives me pleasure to learn that the improvements, which I 

 have merely suggested as deductions from the principles of the inter- 

 ference of induced currents (76), should be in accordance with the ex- 

 perimental conclusions of the above named philosopher. 



