PSYCHOLOGY OF PRESTIDIGITATION. 567 



the king was transformed into the ace of spades. There were four of 

 us j)resent — men accustomed to observation. We were dumfounded 

 and absohitely unable to understand how it was accomplished. The 

 disappearance of the cage was also performed for our benefit by Mr. 

 Arnould. This trick also produced a most curious illusion, though not 

 so forcible as the iireceding one. We can not dispute the fact that the 

 rapidity with which the movement is made is the cause of its invisi- 

 bility. The proof is that should the artist consent to go through the 

 operation slowly we would have no difficulty in detecting the mechan- 

 ism. But at the same time it must be observed that the question is 

 very complex. The invisibility is not dei)endent solely upon the short 

 duration of the sensation received l)y the eye. Numerous experiments 

 have been made in late years in order to measure the time necessary 

 to perceive a letter or a color. The experiment has been made by 

 placing the observer behind an aperture, the opening and closing of 

 which can be regulated. To perceive and recognize a letter it requires 

 some hundredths part of a second. In witnessing a trick the dilSculty 

 of perception is even greater than to recognize a- letter or color, for we 

 must be able to understand and divine the mechanism of an act often 

 very complicated, as " le saut de coup des deux mains." The time this 

 operation occupies, though much longer than would be necessary for 

 us to perceive a color (it occupies fifteen hundredths of a second), is 

 not sufficient for the spectator to grasp it. There are, then, two causes 

 which concur to i^roduce the illusion — the rapid movements of the 

 hands and the comi^licated and inexplicable character of the operation. 

 From the time this second cause of the illusion is done away with the 

 illusion disappears. The artists, whose names I have just mentioned, 

 having been good enough to decompound their movements, I could 

 afterwards, when they went through the trick with their accustomed 

 rapidity, account for each movement of their hands; I saw the move- 

 ment because I had learned to know it, and consequently I knew the 

 exact points to which I should pay the most attention. 



It is by considerations of this sort that we explain what I will call 

 "the screen system." There are an indefinite number of tricks in which 

 to render an object invisible we hide it entirely, absolutely, by placing 

 it behind another object Avhich forms a screen. At first sight it seems 

 impossible that the spectators do not suspect the artifice. But they do 

 not, as in everyday life we are constantly losing sight of the object at 

 which we are looking, and we fill up these short eclipses of the object 

 by a rapid reasoning; if, for instance, while watching a little child 

 playing at ball we suddenly lose sight of its hand, it would seem ridic- 

 ulous for us to conclude that the child had suddenly become one-handed. 

 A detailed mental inuige which remains constantly alive completes the 

 sensation and prevents our taking note of the gaj). The artifice of the 

 prestidigitator consists in taking advantage of such gaps; he surrounds 

 himself with certain material conditions which, for a very short sx)ace 



