ELECTEIC WHIRL. 



605 



The mutual repulsion between the particles of air 

 and the point can be made to move the point itself. 

 The c electric whirl/ fig. 319, J., consists of an easily 

 moveable cross made of very thin sheet brass, the ends, 

 which are pointed, being all bent in the same direction. 



FIG. 319 (A an. proj. ; A and B \ real size). 



When placed with the middle upon the point of a darning 

 needle, of which the eye-end is fixed in a cork in the 

 upper opening of the conductor, the arms revolve in the 

 direction of the arrows when the machine is worked. 



In a very thin sheet of brass a small cavity is pressed with the 

 centre punch, and placing one point of a pair of compasses into the 

 cavity as centre, a circle is drawn on the sheet with a radius of 5 or 

 6 cm . The cross is supported afterwards by placing the cavity upon 

 the point of the needle. The cross is cut as in fig. 319, B. The 

 arms of the cross, which become bent in the cutting, are softened 

 over the lamp, straightened, and bent near the middle, as shown at 

 A in the figure. The side which is uppermost in J5, is obviously 

 the lower one in the experiment. In cutting, care must be taken 

 that clean edges are obtained ; any rough portions must be care- 

 fully filed smooth and even. 



