velocity of the stream, little or none being found where there is no sensible current, seems in some degree to countenance the above idea,

I cannot learn that any experiments have ever been instituted on this subject, though it seems that they might easily be made by a person conveniently situated, and possessed of the requisite instruments. A careful examination, by properlycontrived thermometers, of the relative temperatures of the air, the water, and the bed of the river, and of the changes undergone by them during the above process, would probably go a great way towards solving the problem. I know no one better qualified for this undertaking than Mr. Knight, if he should at any future period have leisure and opportunity to direct towards it the same acuteness of observation and accuracy of investigation which have enabled him to make such important discoveries in the economy of the vegetable kingdom. And, if the explanation of this phenomenon should ever lead to results of any importance to the cause of science, I shall feel sufficiently satisfied, if it be deemed that I have been of any service in pointing out the way.

Blackburn, Lancashire, May 16th, 1818.

1

RICHARD GARNETT.

ART. X. On the Sounds produced by Flame in Tubes, &c. by M. Faraday, Chemical Assistant in the Royal Institution.

THERE is an experiment usually made in illustration of the properties of hydrogen gas, which was first described by Dr. Higgins, in the year 1777,* and in which tones are produced by burning a jet of hydrogen within a glass jar or tube. These tones vary with the diameter, the thickness, the length, and the substance of the tube or jar; and also with changes in the jet. They have frequently attracted attention, and some attempts to explain their origin have been made.

• Nicholson's Journal, Vol. I. page 130.

After Dr. Higgins, Brugnatelli in Italy, and Mr. Pictet at Geneva, described the experiment, and the effects produced by varying the position and other circumstances of the jet and tube; and M. de la Rive read a paper at Geneva (published in the Journal de Physique LV. 165.) in which he accounted for the phenomenon by the alternate expansion and contraction of aqueous vapour. That they are not owing to aqueous vapour, will be evident from some experiments to be described. I have no doubt they are caused by vibrations, similar to those described by M. de la Rive; but the vibrations are produced in a different manner, and may result from the action of any flame.

I was induced to make a few experiments on this subject, in consequence of the request of Mr. J. Stodart, that it shouid be introduced at one of the evening meetings of the Members and Friends of the Royal Institution; and was soon satisfied that no correct explanation had been given. That the sounds were not owing to any action of aqueous vapour, was shewn by heating the whole tube above 212°; and still more evidently by an experiment, in which I succeeded in producing them from a jet of carbonic oxide. That they do not originate in vibrations of the tube, caused by the current of air passing through it, was shewn by using cracked glass tubes, tubes wrapped up in a cloth, and, I have obtained very fine sounds by using a tube formed at the moment by rolling up half a sheet of cartridge paper, and keeping it in form by grasping it in the hand. The sounds have been accounted for, as well as their supposed peculiarity of production by hydrogen, by the supposition of a rapid current of air through the tube; but that this is not essential, is shewn by using tubes closed at one end, and bell glasses, as described by Mr. Higgins, in his first experiment.

I was surprised to find, on my first trials with other gases, that I could produce those sounds from them which had been supposed to be generated exclusively by hydrogen; and this, with the insufficiency of the explanations that had yet been given, induced me to search after the cause of an effect, which appeared to be produced generally by all flame,

In examining attentively the appearance of a flame when introduced into a tube, it will commonly be found, that, on coming within its aperture, a current of air is established through the tube, which compresses the flame into a much smaller space; it is slightly lengthened, but its diameter is considerably diminished: on being introduced a little further, and as the tube becomes warm, this effect is increased, and the flame is gradually compressed a little above its commencement at the orifice of the jet, more than at any other part; a very faint sound begins to be heard, and as it increases, vibrations may be perceived in the flame, which are most evident in the upper part, but frequently also perceptible in the lower and smaller portion; these increase with the sound, which at last becomes very loud, and if the flame be further introduced into the tube, it is generally blown out. Such are the general appearances with hydrogen. If a jet of olefiant, or coal gas, both of which I have ascertained may be used successfully, be substituted; then, in addition to those appearances, it will be perceived, that as the bright flame of the gas enters the tube, its splendour is diminished, and it burns with less light.

By substituting other gases and inflammable vapours for hydrogen, and using other vessels than tubes, I was enabled so to magnify the effects, as to perceive more distinctly what took place in the flame at these times; and soon concluded, that the sound was nothing more than the report of a continued explosion.

Sir H. Davy has explained the nature of flame perfectly; and has shown that it is always a combination of the elements of explosive atmospheres. In continued flame, as of a jet of gas, the combination takes place successively, and without noise, as the explosive mixture is made. In what is properly called an explosion, the combination takes place at once throughout a considerable quantity of mixture, and sound results from the mechanical forces thus suddenly brought into action; and a roaring flame presents something of the appearance of both. If a strong flame be blown on by the mouth, a pair of bellows, the draught of a chinney, or other

means, the air and the gaseous inflammable matter are made to mix in explosive proportions in considerable quantities at once, and these being fired by the contiguous flame, combine at once throughout their whole extent, and produce sound: the effect is rapidly repeated in various parts of the flame as long as the air is mixed thus forcibly with it, and a repetition of noise is produced, which constitutes the roar.

Now this, I believe, to be exactly analogous to that which takes place in what have been called the singing tubes; but in them the explosions are generally more minute and more rapid. By placing the flame in the tube, a strong current of air is determined up it, which envelopes the flame on every side. The current is stronger in the axis of the tube than in any other part, in consequence of the friction at the sides and the position of the flame in the middle; and just at the entrance of the tube an additional effect of the same kind is produced, by the edge obstructing the air which passes near it; the air is therefore propelled on to the flame, and mingling with the inflammable matter existing there, forms portions of exploding mixtures, which are fired by the contiguous burning parts, and produce sound, in the manner already described, with a roaring flame; only, the impelled current being more uniform, and the detonations taking place more rapidly and regularly, and in smaller quantities, the sound becomes continuous and musical, and is rendered still more so by the effect of the tube in forming an echo.

That the roaring flame gives sound in consequence of explosion, can hardly be doubted; and the progress from a roar to a musical tone, is easily shewn in the following manner: take a lamp with a common cotton wick, and trim it with ether or alcohol; light it, and hold a tube over the flame (that which I have used is a thin tube of glass about an inch in diameter; and near thirty inches long ;) in a few seconds after introducing the flame, the draught will be sufficiently strong to blow it out, but if the current be obstructed by applying the fingers round the lamp at the bottom of the tube, combustion will go on, though irregularly; then, by a little management in admit

ting the air on one side or the other, and in greater or lesser quantity, it may be impelled on to the flame in various degrees, so as to produce a rough roaring sound, or one more continued and uniform, of a higher note, and more musical; and these may be made to pass into each other at pleasure: then, by substituting a stream ef etherial vapour for the wick, which may be easily done from a small flask through a tube, the tones may be brought out more and more clearly, until they exactly resemble those of hydrogen.

A similar experiment may be made with coal gas; light a small Argand burner with a low flame, and bring a glass tube, which is very little larger than the diameter of the flame, down upon it so as nearly to include it: the current of air will be impelled on the external part of the flame, it will remove the limit of combustion a little way up from the burner, that part of the flame will vibrate rapidly, burning with continued explosions, and an irregular tone will be obtained. Remove the burner, and fix on a long slender pipe to the gas tube, so as to afford a candle flame that may be introduced into the tube; light it, and introduce it about five or six inches, and a clear musical tone will be obtained.

During the experiments that were made in consequence of this view of the subject, many appearances occurred which might be added to the above account, to support the opinion that the vibration of the flame, in consequence of rapid successive explosions, is the cause of the sound; but they are neglected, because they are supposed unnecessary.

If the explanation given be true, then the only requisite to the production of these sounds is the successive sudden inflammation of portions of gaseous explosive mixtures. These mixtures are most easily made by propelling a stream of air on to a stream of inflammable gaseous matter; but it is also possible to make them in other ways, and the same phenomenon may be produced in a different manner.

That the tube is not essentially necessary, is shewn by making it swell out into a cylinder of three or four inches diameter, except above and below; or part of it may be extended into a