Imatges de pÓgina
PDF
EPUB

But while this circumstance proves to us, that the volcanic action below was much more general than the bare inspection of the emerged part of St. Helena would, perhaps, have allowed us to have calculated; it most forcibly reminds us of the great similarity which exists between this portion of the world and others where volcanic eruptions have taken place—I mean the very extended action of subterranean fires. Etna, with its Lipari, Vulcano, and Stromboli; Hecla with its submarine eruptions at eight miles distance, and at even seventy; and the isles of France and of Bourbon, immediately present themselves as good illustrations of this fact.

That any one should be influenced in his decision respecting the volcanic origin of St. Helena by the supposed former existence of the "Atlantis" is somewhat singular. Geological arguments, and not literary, are alone to be made use of in the question now under consideration; and literary shall I indeed esteem them until the real existence and true geographical situation of this great island of Plato be clearly demonstrated and indisputably pointed out,-whether it may be in Sweden and Norway, according to Rudbeck; in the frozen ocean, according to M. Bailli, or in the Utopian land of fable, according to the more reasonable opinion of Sir William Jones.

But it is fit that these few, and perhaps too general, remarks should be brought to a close, and I would do so without asserting dogmatically the necessary tendency of the evidence resulting from them; for whether this hypothesis, respecting the formation of St. Helena, carries with it any plausibility, or the observations which a perusal of the ideas of others have elicited possess any value, I leave entirely to the reader's decision. I offer them diffidently, desirous rather of leading others to make this singular island an object of philosophic investigation, than anxious to make converts to any peculiar views I may be thought to have entertained upon the subject.

200

[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]

"Re

Refutation of the Charges contained in Mr. Ivory's marks," &c. in the Philosophical Magazine and Annals for February lust.

!

FROM looking into Mr. Ivory's remarks, I find they have assumed that form which all his controversial discussions do when he has the wrong side of the question; which, in the present instance, he has in a superlative degree-for the doctrines which he compels himself to maintain are of the most untenable and contradictory description: but no matter for that, he must still keep up the farce and repeat the old chorus. In such circumstances, as is well known, Mr. Ivory labours hard, by a variety of ways, to obscure the subject, to divert the reader's attention from the real merits of the question, and to excite the indignation of the public against his opponent, by alleging no matter on how ridiculous, frivolous, or unfounded grounds that some advantage has been taken of himself—that some fraud has been committed; such as, in my case, "giving to Mr. Ivory's formula any shape I please,"-using the black art of "legerdemain,"-" playing tricks with the algebraic expressions," &c.

Charges like these, when true, call for exemplary visitation, especially playing off legerdemain with such a grave gentleman as Mr. Ivory; but as I am not aware of having practised any thing of the sort, and as no intelligible evidence is offered of my having played any tricks, I neither see cause for apology, nor need for reform. On the contrary, it is easy to show the futility of all these accusations, and that they may, with far greater justice, be charged upon their author. Indeed, in this case there is no need for playing tricks, or resorting to any unfair means whatever; for let Mr. Ivory take up any position he pleases, provided he retain, as he still obstinately does, hist favourite but incompatible assumptions, and it is easy to prove the extravagant inconsistency of his doctrines, whether among themselves or with the best known facts.

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.

66

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 V' be the initial volume of a mass of air, and V any other volume to which it is to be reduced, while g' and ę 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

(448° + t );

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

[ocr errors]
[merged small][ocr errors][merged small][ocr errors][merged small][merged small]

V

* (448° + t) (1− ) = ↓ (448° + i ) × Œ1

t

;

?

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 'to V, or the density from g' to g; namely,

"

1 (1+0) (-1) = 1 (1+0) (& − 1)

B

1

1

where 6 is the Fahrenheit temperature

a

=480° and

=180°;

whence the formulas become

V

† (480" + 6) (√, −1) = ↑ (490° + ♦ ) (2—1).

6

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 half of V'or e double of g' and 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.

ę

This strange discordance seems to owe its origin to the fol

i

1

1

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.

A

!! X

200

1

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.

1/ ten!! 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 allegations? Is it not highly creditable to Mr. Ivory's talents and veracity to be able to bring forward all these accusations with

**

ut 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 lain very near Mr. Ivory's heart, when, for want of every adD'ab on 8 I 87 thecoup5 to 287Bands 9m als 2 doutor a molt ben ; bu zd › le68,090 8 7us ni Form

T

BEST

< 15

« AnteriorContinua »