136 
YOUNG SCIENTIST. 
The Ilusions of Touch. 
WE all know the deceptions to which 
we are liable from illusions of sense- 
The skilful ventriloquist finds no diffi- 
culty in deceiving our sense of hearing, 
and the errors which we make when we 
trust to our sense of sight are like the 
auctioneer's catalogue—" too numerous to 
mention." Our sense of touch, however, 
has hitherto maintained a character above 
reproach ; when we are in doubt as to the 
reali+v of anything which we see, or even 
first, and place them on the ball, as we 
have figured it. If the pea or ball be now 
rolled about, the sensation is apparently 
that given by two peas under the fingers, 
and this illusion cannot be dispelled by 
the aid of the other senses, as is usually 
the case under similar circumstances. 
We may try and try, but it will be only 
after considerable experience that we 
learn to disregard the apparent impres- 
sion of two objects. 
The explanation is simple enough. In 
the ordinary position of the fingers the 
ILLUSIONS OF TOUCH. 
in regard to its shape, consistence or num- 
ber, an appeal is at once taken to our 
sense of touch, and when " we have felt 
it," argument is at an end. 
But even this severely accurate sense is 
liable to deception, as the following sim- 
ple experiment will show : Take a pea or 
a small marble or bullet, and place it on 
the table or in the palm of the left hand. 
Then cross the fingers, as shown in the 
engraving, the second finger crossing the 
same ball cannot touch at the same time 
the exterior sides of two adjoining fingers. 
When the two fingers are crossed the 
conditions are exceptionally changed, but 
tfie instinctive interpretation remains the 
same, unless a frequent repetition of the 
experiment has overcome the effect of 
our first education on this point. The 
experiment, in fact, has to to be repeated 
a great number of times, to make the 
illusion become less and less appreciable. 
