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temperature could not be thereby raised from 32° to 212°; nor could the ignition of tinder be caused by the heat evolved from air on its being condensed.

But though such results be out of all shape, yet the law now stated is, if possible, still more at variance with itself than with facts; for we soon obtain a very different result, by taking the condensation at several successive steps. Thus, by doubling the density of air at 32° Fah., or putting = 32° and g = 2, we obtain i 90°, which raises the temperature to 122°. Doubling again the density with r = 122° and g = 2, we get i= 106.875. The density has thus been only quadrupled, and yet the rise of temperature, viz. 90° + 106°.875 = 1960.875, exceeds the rise due to compressing all the air of the atmosphere into a point, at one operation*. I may remark, by the bye, that so far as is yet known, an elastic fluid cannot be liquefied by condensation, if it lose no heat.

If the air, which, by having its density quadrupled, has attained the temperature of 228°.88, be now restored to its original density, ought it not to be, in every other respect, restored to its former state? and, in particular, if it have neither gained nor lost heat, ought it not to resume its original tempe→ rature of 32° ? So far, however, from this being the case, we shall find that by restoring the original density, the resulting temperature will be lower than 32° by the enormous quantity of 564°.6. Thus, putting = 228°.88 and

P=

=

1, (for the

law being general, must suit any initial temperature or density,) we obtain i 761°.48. Hence, in place of 32°, the resulting temperature is 228°.88 761°.48-532°.6 Fah., or 84°.6 below the absolute, zero of those who, with Mr. Ivory, insist on an air-thermometer being the standard!

..What a striking contrast between such absurdities and the following formula, in which not the slightest inconsistency can be detected, viz.

i = (448° + 7) (p3— 1).

It is obvious that we may proceed in strict conformity to this law, and yet vary the result considerably; nay, in some cases, enormously, at pleasure, according to the number or magnitude of the parts into which we subdivide the whole change of density as taking place at successive steps.

This Mr. Ivory has rejected, without showing cause why. Most probably he did not like it after it was well known not to be his own production, and especially after I had advanced so much in its favour. Except the index of e, it is M. Poisson's g, formula. The reasons why that index should be are given in Edin. New Phil. Jour. vol. ii. 333, 391, and iv. 101.

I formerly remarked that the notes of music afforded no satisfactory proof that sounds of all intensities are propagated with equal velocities. Another alleged proof, apparently of more weight, has been drawn from the experiments made in France in 1822; where the velocity of sound appeared to be the same, whether the guns were charged with two or with three pounds of powder. When, however, as was the case there, the powder has almost nothing to propel, a considerable proportion of it escapes without catching fire, and so much the more as the charge in the same size of gun is greater: so that the reports from the two and the three pounds of powder, might not differ materially in sharpness. Nor can I attach any stress to equal or uniform velocities deduced from hypothetical data; for we have seen that one of the most natural and obvious inferences from the projectile theory just discussed, is that the velocity ought to decrease rapidly; which is curious enough when we recollect that those who follow this mode of investigation assume, without hesitation, that it accords with a uniform velocity. No solution of the problem can be legitimate, if it take for granted an element so important, but so dubious, as uniformity of velocity,—an element which, I presume, can only be settled by experiment. For, I think it will be found that in solutions of this problem, the uniformity of the propagation of sound, or its independence of intensity, is, at best, assumed, or not provided for. In some cases, as we have seen, it may be got over quietly by inaccurate working; by repeatedly rejecting terms from the calculus, without giving any good reason, or showing that such terms could not have influenced the result,

If the velocity of sound be really greater when it is more intense, then all attempts to bring out a legitimate and definite mathematical result must necessarily prove abortive; because the intensity, being of an indeterminate character, cannot, as

the supposed case would require, be made the basis of mathe matical investigation. The great Euler, to whose sagacity we owe so much, was of opinion that the motion of sound is affected by its intensity. Lagrange, however, thought it easy to show, from theory, that this could not be the case. But, besides the particulars noticed in the present article, the cir cumstance, which I formerly mentioned, of wind exercising such an absolute control over the intensity of sound, and which our refined theories do not recognise, sufficiently shows how little confidence is due to theory in any such matters. The excess of the velocity of sound, aided by a very faint breeze, while passing from Montlhery to Villejuif, on the 22d June, 1822, over its motion on the preceding day, rather favours the opinion that wind adds more than its own motion to that of sound. Further experiments are, however, wanted to decide. this point,

Description of a Regulating Valve for a Gas Establishment. 101, Mount-Street, Grosvenor-Square, August 29th, 1828.

SIR,

The continued and increasing employment of gas, as a source of artificial light, confers a value upon every means which renders its distribution more convenient and economical.

As the consumption of gas, during the night is variable, it is desirable that the pressure at the gas-station should be regulated according to the demand. I have obtained from Mr. Eastwick (the very intelligent engineer of the Bath gas works) a description of a valve which enables him to adjust the flow of gas into the "main," so as to ensure an economical, yet sufficient, supply to the burners at the different periods of the night.

If you think it deserving a place in your Journal of Science, it is much at your service: I therefore enclose it for your approval.

I am, Sir, yours, truly,

R. ADDAMS.

To W. T. Brande, Esq.

"Gas Works, Bath, June 1st, 1828.

"SIR,

"AGREEABLY with your request, I send you a drawing of the index of a regulating valve, which I placed on the eight

inch main pipe leading from these works last summer, and which I had the pleasure of showing to you when you were in Bath in January last.

"The valve consists of a circular plate of metal, nine inches in diameter, sliding over the mouth of the main pipe, in a chamber. The face of the index is a representation of the valve itself; so made in order that the superintendent may know the precise position of the valve at any time.

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"The black disc A is a thin plate of metal attached to a rod coming up from the valve behind the index frame, in which there is a slit for the pin which carries the index to pass. The portion of the circle B, which is uncovered by the disc, represents the aperture, or gas-way into the main pipe. D is a pressure gauge connected with the main on the gasometer side

of the valve, and C, another pressure gauge, also connected with the main on the town side.

"There is a burner, supplied from the town side of the valve, placed before the eye of the person who adjusts the valve.

"From repeated inspection of the town lights at all hours of the night, as well as of the burner before the index, the requisite pressure is known and regulated; as the night advances, the valve is lowered more and more, and in the morning (when the lamps ought to be all out) it is depressed to one-tenth of an inch; that being sufficient to cause the exit of the gas in the lowest situations.

"The operation of the valve is so well understood, that I have been enabled to leave the management of it to the workmen ever since its erection.

"By this simple, yet effectual, contrivance, the saving of gas has been very great.

"I have never had occasion to elevate the valve more than ths, as shown in the drawing, this being sufficient for the escape of upwards of 7000 cubic feet of gas per hour, without the pressure of the gas being reduced more than th of a inch, (viz. from one inch to ths after it has passed the valve.)

“I believe you are aware that, from the nature of the coal used at this establishment, the retorts, after much use, become lined with a hard carbonaceous substance, of so considerable a thickness, as to diminish their capacity to one half and less, on which account a larger number of retorts was required ; and from the imperfect conducting power of this incrustation, the decomposing process was slower, and additionally expensive. I am happy to inform you, that I have perfectly succeeded in removing the incrust in the following way: the retorts are left open, and kept at a good heat, by which the carbonaceous lining undergoes slow combustion, and in the course of a week, or more, according to the thickness, it is entirely burnt away. "Believe me to be, Sir,

"Very respectfully yours,

"To R. Addams, Esq."

"W. H. EASTWICK."

* When the area of the lunaric aperture is 14.733 square inches. R. A.

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