The first charge preferred against me-a serious and criminal one too, had there been the shadow of truth in it-is, that

I am bent on giving to what I call Mr. Ivory's formula any shape, and on making any use of it I please," &c.

As a complete refutation of this grave accusation, I need only observe, that throughout the whole of my reply I have never once mentioned any such formula of Mr. Ivory's, far less turned it into my own shapes: being well aware how different his formulas are from his new law of condensation, which, and not his formulas, was the thing I then wished to discuss. For this reason I kept clear of Mr. Ivory's ever-changing formulas altogether, and employed a formula of my own framing, which, as I shall presently show, fairly and faithfully represents his new law of condensation, while his own formula does not. His celebrated new law is, that "the heat extricated from air when it undergoes a given condensation is equal to of the diminution of temperature required to produce the same condensation, the pressure being constant."

To obtain a formula which shall fairly express this law, let 'be the initial volume of a mass of air, and any other volume to which it is to be reduced, while g and g are the corresponding densities. Then, as is well known, the volume of a mass of air under a constant pressure varies as its temperature reckoned from -448° F., or as 448° +t; where t is the degree on Fahrenheit's scale. The volume would therefore be diminished from V' to V, or the density increased from g' to g, under a constant pressure, if we diminished its temperature reckoned from 448° F. in the ratio of V' to V, or made it equal to

V
Ꮴ

(448°
448° + t );

so that the diminution of temperature required to produce the given condensation is

t

1.

V

↓ (448° + €) (1− ) = ↓ (448° + é)× ➡;

8

the very formula which I formerly employed, without ever giving Mr. Ivory the credit of framing it.

We have thus again arrived at that notable formula expressing Mr. Ivory's new law of condensation, from which there emanates such a catalogue of unparalleled results. Among these, as I formerly shewed, we have tinder kindling at a temperature below that of boiling water-a cold below absolute cold-a greater heat caused by twice doubling the density of a small quantity of air, than if all the air in the universe were instantly condensed into a point!

It remains to be shewn that Mr. Ivory's own and evervarying formulas do not accord with his new law. Towards the bottom of page 105 he gives the following formulas, for the change of temperature due to changing to volume from V' to V, or the density from g' to g; namely,

1

1 (1+0) ( − 1 ) = (1+0) ( − 1 )

В

a

Ө

↑ (480° + 6 ) ( − 1 ) = ↑ (480° + 6 ) (2—1).

Now when Mr. Ivory announced his new law, Phil. Mag. for Feb. 1827, page 94, he illustrated it by an example; where the volume is to be halved and the initial temperature is 32° F.; whence he declares the rise of temperature due to halving the volume to be 90°. But if in the last formulas we make V half of V' or ę double of g' and 0 32°, we do not obtain 90° but 96°. A clear proof that Mr. Ivory's own formulas are very different from his new law, though they involve as great absurdities.

This strange discordance seems to owe its origin to the fol

lowing circumstance. For the sake of obscurity, and lest any one should easily read through his untenable doctrines, Mr. Ivory is perpetually shuffling his formulas, and substituting one for another in endless succession. He is, moreover, continually shifting between Fahrenheit and the centigrade scale; so that he never writes two papers in succession where he uses the same scale of temperature. It is of no moment which of the two scales be employed; but Mr. Ivory knows well that it is a sad embarrassment to the reader to shuffle between them. Now it, would appear, that, in thus zealously endeavouring to make the reader lose sight of the subject, Mr. Ivory has deservedly fallen into his own snare, so as to commit the blunder above mentioned.

I am called upon, it seems, to go back to the principles from which Mr. Ivory's formula is deduced, and to his usual theory of the thermometer. On this head I need only refer him to my other paper, which, I presume, will appear along with this. In it he will have an additional opportunity of seeing an exposure of the utter inconsistency of these principles, and therefore any deduction from them must be of very little worth, however anxious he may be to keep up the farce a little longer. If a formula be in itself absurd, it little matters from what it be deduced, for that cannot legitimize it. But one thing is now evident, and that is the grand point at present, that, without calling it Mr. Ivory's formula, I had used a formula which faithfully represents his new law of condensation, with all its concomitant absurdities.

Where, then, is the shadow of evidence of my having, in the least degree, changed the shape of Mr. Ivory's formula-of legerdemain-playing tricks, and such like ridiculous allega tions? Is it not highly creditable to Mr. Ivory's talents and veracity to be able to bring forward all these accusations without accompanying them with one syllable of proof? He has announced that he will not again return to the subject. There are few, I dare say, but will admit that it is high time he should retire, unless he have something more substantial than mere ipse dixit to bring forward. This dispute must surely have very lain very near Mr. Ivory's heart, when, for want of every ad

1

missible argument, he has been laid under the necessity of advancing so many unsupported, nay unfounded, statements, by way of defence. There is one consideration, however, which even in retiring must afford him no small consolation, namely, that he had the honour of beginning this controversy himself.

In conclusion, I only beg to recall the attention of Mr. Ivory and others, who dote upon the analytical theory of sound, to an objection I formerly stated, and which, so far as I know, had not been before attended to; namely, that in all these fluxionary investigations, each small cylinder of air is supposed to vibrate so as to have its variable length exactly proportional to its velocity in every part of a vibration. Consequently, when the velocity becomes nothing, at the turn of each vibration, the length of the cylinder is also nothing; that is, the cylinder is annihilated at the turn of each vibration. Now, I would ask these philosophers, if this circumstance alone would not be fatal to the fluxionary investigations, although all other objections were laid aside?

HENRY MEIkle.

A New System of Geology, in which the great Revolutions of the Earth, and Animated Nature, are reconciled at once to Modern Science and Sacred History. By ANDREW URE, M.D., F.R.S., &c. London: Longman, Rees, Orme, Brown, and Green. 8vo. pp. 680; with seven plates and fifty-one wood-cuts. 1829.

WE gladly embrace the earliest opportunity of presenting our readers with an analysis of this interesting, and in many respects original, work. The author has been long esteemed among men of science for his able and intrepid refutation of numerous errors current in some of our chemical systems; 'and' he has now directed, with a no less steady aim, the same vigi-' lance of observation and logical acumen towards the mystifi cations of the mineral world. Though the book now before us has not in the least a controversial texture, yet its author could not possibly avoid noticing, in his introductory dissertation, the chimæras of cosmogony which at no distant date fluttered in many a geognostic head; and there is something

JAN. MARCH, 1829.

I

truly picturesque in the athletic nonchalance with which he strangles them at a grasp, instead of nibbling at their wings and claws, as the rival partisans of those reveries were wont to do.

But Dr. Ure's present labours are not all of the Augean kind. Not content with removing much of the rubbish which has been heaped around rational geology, he has apparently got a glimpse of the true architecture of the globe, and has delineated some of its outlines with a powerful hand.

The great mystery of the mineral kingdom is to be found in the remains of the tropical plants and animals so profusely buried in the secondary and diluvial strata, not only of our temperate countries, but of even the circumpolar zones. Their delicacy of fabric, integrity of form, and posture in the earth, repel the idea of their having been transported to their present sites from the distant equatorial regions, by any aqueous catastrophe. They are undoubtedly buried in the spot where they grew and perished. It is to this enigma of the high temperature which anciently prevailed in our parallels of latitude, that Dr. Ure has concentered all his faculties of research and illustration, and to certain sudden crises of refrigeration which seem to have supervened at distant intervals, the last of them being the Noachian Deluge. That prior to this event, the terraqueous equilibrium was unstable, many great geological phenomena clearly attest; and the Doctor, in discriminating them, endeavours to shew whence that instability proceeded.

These propositions, as now picked out by us in an insulated form, may have somewhat of a hypothetical aspect, but no such impression will be felt in studying the work itself, since they spontaneously result from the phalanx of facts which he has embodied in their service.

There is one thing which we like exceedingly in the Doctor's schemes of induction: the documents subservient to them are neither got up nor trimmed by himself, but are taken, without distinction, from every record of genuine observation, whatever may have been the theoretical creeds of their authors.

It is amusing enough in this tesselated scheme of induction, to see conclusions legitimately drawn from facts which were originally advanced in support of entirely different views. But such is the influence of our author's logical collocations, that we can rarely help assenting to them, as highly probable, at least, if not absolutely true; and this is nearly as much as can be said for all physical doctrines not directly drawn by geometry from observation or experiment.