OP ARTS AND SCIENCES. 



281 



XXTIT. 



A NEW FORM OF INDUCTIVE APPARATUS. 



Bt Henry P. Bowditcu. 



Presented, Oct. 12, 1875. 



The inductive apparatus commonly used in physiological laboratories 

 is the so-called " Sledge Apparatus " of Du-Bois Reymond. In this 

 instrument, the intensity of the induced current is regulated by varying 

 the distance between the two coils, their axes being always kept in the 

 same straight line. By this method, very feeble currents can only be 

 obtained by separating the coils to a considerable distance, and an in- 

 strument made to permit this separation has often an inconvenient 

 length. 



In the instrument here presented, and which is figured in the 

 accompanying wood cut, this ditficulty is obviated by allowing the 

 secondary coil, as soon as it has been withdrawn enough to be fairly 

 free of the primary coil, to rotate round a vertical axis. In this way, 



the intensity of the induced current may be reduced to any desired 

 degree, zero being obtained when the coils are at right angles to each 

 other. The effect of simple rotation of the secondary coil, regarded 

 by itself, would doubtless be to cause the intensity of the induced 

 current from that coil to vary in the same proportion with the cosine 



