544 



Messrs. A. Bursill and H. Bedson 



On a 



The flexible leads are now removed and the handle turned 

 until the armature readies its maximum speed and the centri- 

 fugal clutch operates. By adjusting the resistance o£ the 



Fii 



-W\Mly- *i 



Connexions for Calibration. 



calibrating coil the pointer of the current-measuring in- 

 strument can now be brought to any desired reading, so that 

 the scale having- been graduated to read flux in C.Gr.S. units, 

 the resistance is adjusted to give the reading representing 

 the known flux through the armature. 



The scale will now be true throughout as the current is 

 proportional to the flux through the armature. 



Tests of Coercive Force. 



In order to test the coercive force of a magnet a set of 

 coils is required and an ammeter in addition to the flux- 

 measurino- instrument already described. Of course there 

 must also be available a source of direct current sufficient for 

 magnetizing and demagnetizing purposes. PL A II. fig. 3 

 shows the complete instrument ready for a test of coercive 

 force. 



The coils are so wound that they can be slipped on to the 

 magnet and fill the whole available space when the magnet 



