Provide a long, flat glass ruler or rod, as in the engraving, and cement it with mastic to the edge of a drinking-glass fixed into a wooden stand; support the other end of the rod very lightly on a piece of cork, and strew its upper surface with sand; set the glass in vibration by a bow, at a point opposite where the rod meets it, and the motions will be communicated to the rod without any change in their direction. If the apparatus be inverted, and sand be strewed on the under side of the rod, the figures will be seen to correspond with those produced on the upper surface.
DOUBLE VIBRATION.
Provide two discs of metal or glass, precisely of the same dimensions, and a glass or metal rod; cement the two discs at their centres to the two ends of the rod, as in the engraving, and strew their upper surfaces with sand. Cause one of the discs, viz. the upper one, to vibrate by a bow, and its vibration will be exactly imitated by the lower disc, and the sand strewed over both will arrange itself in precisely the same forms on both discs. But if, separately, they do not agree in their tones, the figures on them will not correspond.
CHAMPAGNE AND SOUND.
Pour sparkling champagne into a glass until it is half full, when the glass will lose its power of ringing by a stroke upon its edges, and will emit only a disagreeable and puffy sound. Nor will the glass ring while the wine is brisk, and filled with air-bubbles; but, as the effervescence subsides, the sound will become clearer and clearer, and when the air bubbles have entirely disappeared, the glass will ring as usual. If a crumb of bread be thrown into the champagne, and effervescence be re-produced, the glass will again cease to ring. The same experiment will also succeed with soda-water, ginger wine, or any other effervescing liquid.
MUSIC FROM PALISADES.
If a line of broad palisades, set edgewise in a line directed from the ear, and at even distances from each other, be struck at the end nearest the auditor, they will reflect the sound of the blow, and produce a succession of echoes: these, from the equal distance of the palisades, will reach the ear at equal intervals of time, and will, therefore, produce the effect of a number of impulses originating in one point. Thus, a musical note will be heard.