6 INTRODUCTION 



based not merely upon the fact that no such signals had 

 been detected by the most expert observers, but also 

 upon the character of the two men who exhibited the 

 horse, upon their behavior during the entire period, and 

 upon the method of instruction which Mr. von Osten 

 had employed. In the case of unintentional signs, on the 

 other hand, one had to deal with the fact with which 

 physiologists and experimental psychologists are es- 

 pecially familiar, viz., that our conscious states, without 

 our willing it — indeed, even in spite of us — are accom- 

 panied by bodily changes which very often can be de- 

 tected only by the use of extremely fine graphic methods. 

 The following is a more general instance : every mother, 

 who detects the lie or divines the wish in the eyes of the 

 child, knows that there are characteristic changes of 

 facial expression, which are, nevertheless, very difficult 

 of definition.* 



The commission did not even maintain or believe that 

 unintentional signs within the realm of the senses known 

 to us, were to be excluded. Professor Nagel and I 

 would never have subscribed to any such conclusion. The 

 sentence in question, therefore, could only be interpreted 

 as follows: that signals of the kind that are used in- 



* " From the productions of the ' thought-readers ' we see how slight 

 and seemingly insignificant the unconscious movements may be, which 

 serve as signs for a sensitive re-agent. But in this case no contact is 

 necessary. There would have to be some sort of visible or audible ex- 

 pression on the part of the questioner. No proof for this has as yet 

 been advanced." 



How any one possessing the power of logical thought could possibly 

 infer from these words of mine (published in the above-mentioned ar- 

 ticle in the " Tag "), that I denied the possibility of the occurrence of 

 visual signs, is to me incomprehensible. What I did dfeny, and still 

 deny, is that up to that time any had been proven to occur. 



