-1830] 



WRITINGS OF JOSEPH HENRY. 



the same direction. Instead of the cylinder, a separate bat- 

 tery of greater power may be used, by suspending the inner 

 coil, as shown in Fig. 9 ; hh are cups with mercury — the 

 upper wire should turn on a fine steel point. 



Fig's 5 and 6, are front and side views of a modification 

 of an instrument, described by Mr. Sturgeon. It consists of 

 a dipping needle, surrounded by a multiplying coil, turned 

 edgewise, but in all other respects similar to that of Fig. 1, 

 If, when the needle is placed in the magnetic meridian, and 

 the coil in the plane of the dip, a galvanic current be passed 

 through it in a direction opposite to that of the sun, the 

 north end of the needle will turn up, as in Fig. 7 ; but if in 



the contrary direction, it will turn down, as Fig. 8. If the 

 coil be placed at right angles to the dip, as shown in the 

 dotted line. Fig. 6, and the current passed in the first men- 

 tioned direction, the needle will not alter its position, but 

 will be more firmly fixed in it: if passed in the contrary 

 direction, it will turn half-way round and dip with its south 

 end. The quadrant q permits the coil to be readily placed, 

 either in the plane of the dip or at right angles to it. 



