air-tight. One of the caps has a small hole drilled through the centre. (See Fig. 44.)
When about to present the trick the two glass caps are laid on the bottoms of two upturned tumblers, where they are quite invisible. The performer then draws attention to two square pieces of paper, which he dips into the water contained in the bowl, afterward laying them 
Fig. 44.—Hydrostatic Tube down on the glass tumblers, and over the glass discs. He next shows the tube, passing his wand through it to prove that it has not undergone any preparation. Then taking one of the papers, and at the same time secretly securing one of the discs (not the one with the hole in it), he places it at the bottom of the tube, which is forthwith stood on the palm of the left hand. The tube is then filled with water and covered with the remaining piece of paper and glass cap.
The position of the tube is then reversed, after which it is taken by the centre and both papers are removed. The water will not run out from the small hole in the bottom cap owing to the fact that no air can get in at the top. The glass caps being absolutely in-
