1 32 RESPONSE IN THE LIVING AND NON-LIVING 



individual magnet. The bar as a whole, nevertheless, ex- 

 hibits no external magnetisation. This is held to be due 

 the fact that the molecular magnets are turned either 

 in haphazard directions or in closed chains, and there is 

 therefore no resultant polarity. But when the bar is 

 subjected to a magnetising force by means, say, of a sole- 

 noid carrying electrical current, the individual molecules 

 are elastically deflected, so that all the molecular magnets 

 tend to place themselves along the lines of magnetising 

 force. All the north poles thus point more or less one 

 way, and the south poles the other. The stronger the 

 magnetising force, the nearer do the molecules approach 

 to a perfect alignment, and the greater is the induced 

 magnetisation of the bar. 



The intensity of this induced magnetisation may be 

 measured by noting the deflection it produces on a 

 freely suspended magnet in a magnetometer; 



The force which produces that molecular deflection, 

 to which the magnetisation of the bar is immediately due, 



is the magnetising current 

 flowing round the solenoid. 

 The magnetisation, or the 

 molecular effect, is measured 

 by the deflection of the mag- 

 netometer. We may express 



FIG. 82. CURVE OF MAGNETISATION tne relation between Cause 



and effect by a curve in which 



the abscissa represents the magnetising current, and 

 the ordinate the magnetisation produced (fig. 82). 



In such a curve we may roughly distinguish three 

 parts. In the first, where the force is feeble, the mole- 



