INTRODUCTORY xxix 



the time, as " parlour tricks," and in making them I had 

 no object other than the amusement of the youngsters. 

 But when upon reversing an apple I obtained a reversal 

 of sign my interest was keenly aroused and a series of 

 experiments was initiated which are described in Part I, 

 and which, so far, touch little more than the fringe of the 

 subject. 



From that time I went on working patiently between 

 intervals of strenuous commercial and professional life, 

 saying nothing, publishing nothing, but collecting data 

 upon which to found a considered opinion and this present 

 volume is the result. 



A. E. B. 



