VERTICAL CURRENTS TURN NEEDLES. 



impinging against the vertical sides of compass- 

 needles, and producing rotation, the writer caused 

 a steel needle to be made, eight inches long, with 

 a width of three-fourths of an inch, and thickness 

 of one thirty-second of an inch, balanced on the 

 point of a sewing-needle, to be mounted either 

 flatwise or edgewise, at pleasure, as represented in 

 Fig. 32. It was an- 

 ticipated that, in ex- 

 tending the area of 

 the vertical currents 

 on the sides of the 

 needle, a more pow- 

 erful electro-mechan- 

 ical action might be 

 developed, producing 

 greater oscillations of 

 the needle. To test this supposition, the magnet 

 was placed flatwise, with the N pole pointing 

 south, and then left free to yield to the action of 

 the terrestrial currents : the number of oscillations 

 was repeatedly counted, and found to be twenty- 

 one in 2.75 minutes, before the magnet came to a 

 state of rest. With the edgewise mounting, it 

 made twenty-seven oscillations, continuing 3.31 

 minutes ; being twenty-nine per cent, more in 

 number, and continuing twenty per cent, longer 

 in time, notwithstanding the greater resistance of 

 the air from the broad side of the magnet. 



Fig. 32. 



