SOURCE OF ORGANIC ENERGY. 33 



The following .quotation is from Professor P. G. 

 Tait's book on the Properties of Matter. It re- 

 lates to an experiment in which a vertical wire, fas- 

 tened above and suspending a heavy weight below, 

 was first twisted and then allowed of itself to untwist 

 and return to its original position : — 



" We have already seen that even brittle bodies 

 may be completely changed in form by small but 

 persistent forces. And there is no doubt that all 

 elastic recovery in solids is gradual ; so that, for in- 

 stance, in the torsion vibrations which we have just 

 considered, even when there is no sensible viscous 

 resistance, the middle point of the range does not 

 coincide with the original untwisted position of the 

 wire. It is always shifted toward the side to which 

 torsion was applied, and to a greater extent the 

 longer the wire has been kept twisted before being 

 allowed to vibrate. With every vibration, however, it 

 creeps slowly back towards the original undisturbed 

 position, but usually comes to rest before reaching it. 

 But even after the oscillations have ceased, the wire 

 still continues to untwist, more and more slowly, 

 sometimes not even approximately reaching its un- 

 disturbed position until hours or even days have 

 passed. 



"These phenomena are seen in a more striking 

 form when we dispense with oscillation. Thus, for 



