To understand the diagrams it will be necessary to remember the following explanations of the letters used in [Fig. 28].
A and B are the hands of the person just described whose thumbs bear the string.
C and D are your own hands, left and right respectively.
E is the hand of a third person who holds the key.
F and G are the two sides of the loop.
Begin by catching the string F on your little finger of C and G on the little finger of D, as in [Fig. 28]. Now transfer the string from the little finger of C to the thumb of B, and thus free your hand C.
Between the forefinger and thumb of B you must take the string G between the key and A.
Now catch this part you have taken round the thumb of B, slip the string from the little finger of D, and when E pulls the key, it will come quite free from the string ([Fig. 29]).
A Sure Eye
Stick a sharply-pointed knife, preferably with a heavy handle, into the lintel of the door, or into a wooden beam upon the ceiling. Then ask for some one with a sure eye to mark the exact spot on the floor by putting a cent upon it, where the knife will drop when displaced.