HINTS FOR PUBLIC SPEAKERS.
In a large room, nearly square, speak from one corner to the other corner, diagonally. In ordinary rooms, the lowest pitch that will reach across the room is best. In the same, speak along the length. Low ceilings carry sound better than the high.
THE MERIDIAN ALARUM.
There are other ways of utilising the burning-glass to give a signal than to adjust it so that the rays, at noon, shall fire off a cannon, as at the Palais Royal, Paris. For instance, let the action of the focussed light and heat operate on a delicate spring retaining the hammer of a bell, the valve of a chamber of compressed air, with its outlet forming a whistle, &c., &c.
MUSICAL WATER.
A jet of water, passing through a hole in a brass plate fixed at the end of a glass tube will emit a musical sound, in consequence of the intermittent flow of the liquid through the orifice. Again, a slender vein of water, some twelve inches long, on being allowed to fall vertically from a vessel, will break at the lower end of the vein into drops. This vein of water should be brightly illuminated from above by a beam of light sent through it from an electric lamp, so that the thread of water will look like a line of light, from the end where it breaks into drops to the orifice from which it issued. A musical note of constantly-increasing pitch being then set up by means of the wind instrument known as a “syren,” when the note reaches a sufficiently high pitch, the sound will act upon the luminous column of water, which will shorten itself by four or five inches, in response to the one particular sound to which it was sensitive. The same jet of water will respond to the beats produced by two organ-pipes, &c.
THE ÆOLIAN WHISTLE.
The Chinese fasten a whistle to their kites, so that the mouth always faces the wind, and the sound is almost continuous.
SIMPLE ÆOLIAN HARP.
Fasten the ends of a length of waxed saddler’s silk to pegs or nails, which insert in the crack between the two sashes midway in a window, so as to stretch the cord well. The entering air will call out the musical vibrations.