The optical method devised by Dr. König, to which he gave the name of manometric flames, consists of bringing the condensations and rarefactions of sound waves to act upon a gas flame and regulate its height, and of observing the effect in a revolving mirror. The principle of the apparatus is shown in Fig. 1, and the complete form in Fig. 2.

A wooden or metal box is divided into two chambers, A and B, by an elastic diaphragm D. Two pipes open into А and one into B. The pipe C brings in gas, which is burned as a small, round flame at the top of the tube Е. The pipe H opens into B and conveys the sound waves made before its open end at M. When D is struck by a condensation, it bends toward A, making that chamber smaller, increasing the pressure, and making the flame burn higher at E. When a rarefaction comes to D, the chamber A is made larger, the pressure is decreased, and the flame drops down to a shorter one. These changes follow one another so rapidly that the eye cannot detect them unless the image of each flame is separated from the others. This can be done in two ways: first, by turning the eye quickly and throwing the line of sight across the flame, when the images will be separated in the eye; and second, by the use of a revolving mirror. If the mirror is turned while the flame is burning steadily, the reflection of the flame seen in the mirror will be a plain band of light; but if a simple

tone is sung into the mouth M, the rise and fall of the flame will show itself as a succession of pointed reflections of equal height, leaning in the direction opposite to the rotation of the mirror, as in Fig. 3, А. If now the octave of this tone is sung, the reflection will have twice the number of points. If the tone sung is accompanied by overtones, the reflection will show a compound form in which smaller waves are impressed upon the fundamental as in Fig. 3, B.

NOTE. - Experiments with vibrating flames and rotating mirror will not give satisfaction unless carried on in a dark room.

Demonstration. - Sing the tones of the scale before the mouthpiece, calling each tone O. Notice the change for each pitch. Repeat with do, re, mi, etc. Can you tell a simple tone from a compound one?

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مواضيع ذات صلة

The Wedge

The Law of the Screw

Systems of Fixed and Movable Pulleys

The Inclined Plane

The Screw

Application of the Screw

The Automobile

Gas Engines

The Pendulum Method traces the curve. Demonstration

Graphical Method of Combining Vibrations

The Vibration of Plates

The Vibration of Rods and Tubes