Take a glass nearly full of water, or other liquor, and setting one hand upon the foot of it to hold it fast, turn slightly one of the fingers of your other hand upon the brim or edge of the glass, (having before privately wet your finger,) and so passing softly on, with your finger pressing a little, then the glass will begin to make a noise, the parts of the glass will sensibly appear to tremble with notable rarefaction and condensation, the water will shake, seem to boil, cast itself out of the glass, and leap out by small drops, to the great astonishment Of the observers, if they are ignorant of the cause, which is only the rarefaction of the parts of the glass, occasioned by the motion and pressure of the finger.