limpid portion became elongated to the extent shown in fig. 134. Fig. 132, it will be understood, represents the vein exposed to the irregular vibrations of the city of Paris, while fig. 134 represents a vein produced under precisely the same conditions, but withdrawn from those vibrations.

The drops into which the vein finally resolves itself, are incipient even in its limpid portion, announcing themselves there as annular protuberances, which become more and more pronounced, until finally they separate. Their birth-place is the orifice itself, and under even moderate pressure they succeed each other with sufficient rapidity to produce a feeble musical note. By permitting the drops to fall upon a membrane, the pitch of this note may be fixed; and now we come to the point which connects the phenomena of liquid veins with those of sensitive flames and smoke-jets. If a note in unison with that of the vein be sounded near it, the limpid portion instantly shortens ; the pitch may vary to some extent, and still cause a shortening; but the unisonant note is the most effectual. Savart's experiments on vertically descending veins have been recently repeated in our laboratory with striking effect. From a distance of 30 yards the limpid portion of the vein has been shortened by the sound of an organ-pipe of moderate intensity but of the proper pitch.

The excellent French experimenter also caused his vein to issue horizontally and at various inclinations to the horizon, and found that, in certain cases, sonorous vibrations were competent to cause a jet to divide into two or three branches. In these experiments, the liquid was permitted to issue through an orifice in a thin plate. Instead of this, however, we will resort to our favourite steatite burner; for with water also it asserts the same mastery over its fellows that it exhibited with

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flames and smoke-jets. It will, moreover, reveal to us some entirely novel results. By means of an indiarubber tube the burner is connected with the water pipes of the Institution, and, by pointing it obliquely upwards, we obtain a fine parabolic jet, fig. 135. At a cer

tain distance from the orifice, the vein resolves itself into beautiful spherules, whose motions are not rapid enough to make the vein appear continuous. At the vertex of the parabola the spray of pearls is more than an inch in width, and, further on, the drops are still more widely scattered. On sweeping a fiddle-bow across a tuning

fork, which executes 512 vibrations in a second: the scattered drops, as if drawn together by their mutual attractions, instantly close up and form an apparently continuous liquid arch some feet in height and span, fig. 136. As long as the proper note is maintained the vein looks like a frozen band, so motionless does it appear. I stop the fork, and now the arch is shaken asunder, and we have the same play of liquid pearls as before. Every sweep of the bow, however, causes the drops to fall into a common line of march.

A pitch-pipe, or an organ-pipe yielding the note of this tuning-fork also powerfully controls the vein. My voice does the same. On pitching it to a note of moderate intensity, I cause the wandering drops to gather themselves together. At a distance of 20 yards, my voice is, to all appearance, as powerful in curbing the vein, and causing its drops to close up, as when I stand close to the issuing jet.

The effect of beats upon the vein is also beautiful and instructive. They may be produced either by organ-pipes or by tuning-forks. Before you are two forks, one of which vibrates 512 times, and the other 508 times in a second. You will learn, in our next lecture, that when these two forks are sounded together we ought to have four beats in a second. I sound the two forks, and find that the liquid vein gathers up its pearls, and scatters them in synchronism with the beats. When standing near the vein we notice a rhythmic movement of the spots of light reflected from it, keeping time with the beats The alternate retreat and advance of the point where the drops are first formed is executed in the same period, and is very beautiful. The sensitiveness of this vein is now astounding; it rivals that of the ear itself. Placing the two tuningforks on a distant table, and permitting the beats to die gradually out, the vein continues its rhythm almost as long as hearing is possible. A more sensitive vein might actually

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prove superior to the ear-a very surprising result, considering the marvellous delicacy of this organ.*

By introducing a Leyden jar into the circuit of a powerful induction coil, I obtain, as those acquainted with the coil well know, a series of dense and dazzling flashes of light, each of momentary duration. I darken the room, and, with a succession of flashes, illuminate the vein. Its drops are rendered distinct, every one of them being transformed into a little star of intense brilliancy. They are scattered widely apart. I call to the jet in the proper tone of voice. It instantly gathers its drops together into a necklace of inimitable beauty. I suspend my voice, the vein goes to pieces; I call again, and the straggling stars arrange themselves once more in succession along the curve. While thus arranged, I gently shake the indiarubber tube which feeds the jet, and obtain interlacing strings of luminous pearls.

In these experiments the whole vein gathers itself into a single arched band when the proper note is sounded; but, by varying the experiment, it may be caused to divide into two or more such bands, as shown in fig. 137. Drawings, however, are ineffectual here; for the wonder of these experiments depends mainly on the sudden transition of the vein from one state to the other. In the motion dwells the surprise, and this no drawing can render.†

* When these two tuning-forks were placed in contact with a vessel from which a liquid vein issued, the visible action on the vein continued long after the forks had ceased to be heard.

The experiments on sounding flames have been recently considerably extended by my assistant. By causing flame to rub against flame, various musical sounds can be obtained, some resembling those of a trumpet, some those of a lark. By the friction of unignited gas-jets, similar though less intense effects are produced. When the two flames of a fishtail burner are permitted to impinge upon a plate of platinum, as in Scholl's 'perfectors,' the sounds are trumpet-like, and very loud.

SUMMARY OF LECTURE VI.

When a gas-flame is placed in a tube, the air in passing over the flame is thrown into vibration, musical sounds being the consequence.

Making allowance for the high temperature of the column of air associated with the flame, the pitch of the note is that of an open organ-pipe of the length of the tube surrounding the flame.

The vibrations of the flame, while the sound continues, consist of a series of periodic extinctions, total or partial; between every two of which the flame partially recovers its brightness.

The periodicity of the phenomenon may be demonstrated by means of a concave mirror which forms an image of the vibrating flame upon a screen. When the image is sharply defined, the rotation of the mirror reduces the single image to a series of separate images of the flame. The dark spaces between the images correspond to the extinctions of the flame, while the images themselves correspond to its periods of recovery.

Besides the fundamental note of the associated tube, the flame can also be caused to excite the higher harmonics of the tube. The successive divisions of the column of air are those of an open organ-pipe when its harmonic tones are sounded.

On sounding a note nearly in unison with a tube containing a silent flame, the flame jumps, and if the position of the flame in the tube be rightly chosen, the extraneous sound will cause the flame to sing.