"Necessity," according to the old adage, "is the mother of invention," and seldom has this truth being more strikingly exemplified than in the present instance. A blocker of the name of Vincent Price, became so afflicted from an aneurism, that he found he must abandon the business unless he could contrive a machine which would effect the pressing without the bodily pressure. He accordingly set about the task, and has succeeded so well as to produce an apparatus, by which, not only the bodily pressure is dispensed with, but twice the number of bonnets is pressed in a given time, that can be turned out of hand in any other way. The Society of Arts (during the administration of Mr. Graham,) awarded to Mr. Price their Silver Medal for his invention; and our present account of it is made up partly from the last Part of their Transactions, and partly from some communications made directly to ourselves by the inventor. A is one of the blocks in position to receive a bonnet: B is the box iron with its handle C, which is hung with double joints and swivel to the lever D, which is connected to the treadle E, by means of the vertical bar of iron F, the weight of which is sufficient to overbalance the box-iron B and the treadle E.

Instead of standing, as usual, the blocker sits on the stool G, and by his feet on the treadle lowers the box-iron, the pressure of which he can vary from an ounce to upwards of 5 cwt., and which he can also guide and turn in any direction by the handle C.

The middle upright bars, H and I of the frame, are made double, to serve as guides to the lever D and treadle E, and also to receive the moveable crossbar J, which supports the block A. When the sides are to be blocked, the axis K is drawn forward out of the metal socket L, and the block A, placed on the end of it. To the axis K is attached an arm M, which is moved by either hand of the blocker, so that the bonnet may be turned quick round under the iron: the arm has a balance weight N.

O O is a net stretched across the whole space before the blocker on which the bonnet may be laid. P and Q are two shelves on which to place blocks of different sizes.

Mr. Price now manufactures the apparatus for the bonnet trade, from which he is deservedly receiving every encouragement. His address is 33, Wardourstreet, Soho.

THE HISTORY OF ELECTRO-METALLURGY,

AND MR. C. J. JORDAN.

Sir, The very flattering manner in which my claims in connexion with the discovery of electro-metallurgy have been recognized in your pages, demands from me a grateful acknowledgment. When my communication of May 22, 1839, appeared in your Magazine, it was submitted to public consideration to avert, as far as possible, a loss of precedence impending on further delay in its publication, coupled with the conviction, that if worthy of attention it would receive it in the end. Although it would be untrue to deny that disappointment was felt at the neglect it met with; yet, to have murmured at the tardiness of public judgment would have been a step without immediate object. Reflecting also, that in whatever light my letter may have been viewed, nothing advanced therein had been disputed, I determined to remain silent on the matter, and wait the arousing of public attention by other hands a consummation which I foresaw must, in some way or other, ultimately take place. The expectation has been realized, and I have been indulged with the accession of a vigorous advocate in one of your ablest correspondents, whose contributions to a "History of Electro-metallurgy" have set the matter in a much clearer light than I feel myself qualified to have done. Whatever may be the relation of this gentleman with other individuals mentioned in his paper, with myself it is purely impersonal. The comprehensive exposition of Mr. Dircks appears to have been dictated solely by an impartial spirit, and a just perception of the merits of the case with a view of eliciting truth, In return for his valuable exertions in my cause, I beg to express my sincere thanks.

It may be necessary to mention here, that at the time of the publication of the second "Contribution," &c., its author was personally unknown to me; but that in consequence of a conversation with Mr. Brown, Librarian to the Mechanics' Institution, I was induced to open a communication with Mr. Dircks, which led to an interview with that gentleman, February 28.

I am fully sensible, Sir, of the honour done me by your concurrence in the conclusion drawn by Mr. Dircks; and I may be permitted to say, that all previous disappointment is amply compensated by

your approval and final decision in my favour-conveyed too in a tone of warm eulogium, most gratifying, as coming from one to whose position and repute in the literature of the arts the highest respect pertains.

In regard to Mr. Spencer, a few remarks may be expected from me: they must at present be brief, and will convey the intimation, that I am as little disposed to view his labours in electro-metallurgy with jealousy, as I am inclined. to relinquish my identification with its discovery. I await with some interest the advent of his promised documents, which are to annihilate all further rivalry-or otherwise. In either event I shall remain satisfied, being conscious of the difficulty he will encounter in extinguishing my claim to the character of an independent originator of this art, or in setting aside my incontestable priority in publication.

I remain, very respectfully, yours,
C. J. JORDAN.

March 8, 1844.

THE DISCOVERY OF ELECTROGRAPHY. Sir, I nowhere find in Mr. Dirck's last communication that he refuses the terms I proposed; but you do, in your editorial capacity, I suppose on his authority; and add, that "I am in no condition to stipulate terms." Indeed! And what was the gist of the proposed terms? That after Mr. Dircks had fully made his charge, I should reply—then submit both cases, after having been printed, to a competent committee, and whatever decision they came to, I should feel myself bound to abide by it-and this is not accepted! I said at the outset, with regard to Mr. Dircks, that I wished I had an opponent of whose honest intentions in the cause of truth I was better assured. I cannot help thinking that if I had had an honest opponent, there could have existed no possible difficulty, in accepting such terms, they being, what all men desirous of settling a matter fairly, readily agree to. There is no man that I would have sooner left it to than yourself, from all I have hitherto seen of your conduct in the Magazine; but, Sir, you can scarcely expect that now, seeing that you have already pronounced an opinion on the matter at issue, and that, too, from only one side of the question, and which, I speak with deference, if you had read carefully, warranted a very different conclusion.

You further add, that it was easy for me. to say when I claimed the invention that I

knew nothing of Mr. Jordan's letter, had never seen it, never read it, never heard of it. I assure you most solemnly I could have said so in the sincere spirit of truth, if I had thought this gentleman's letter in any degree affected my claims, after having read it the other day in your Magazine, for the first time.

You also seem to be in much haste to see my reply-so does Mr. Dircks. I really do not see why I should withhold it now, unless it be to insure fair dealing, and perhaps let Mr. Dircks save me trouble-as he has half done already-which a careful analysis of his papers will show; however, let my reply come when it may, depend on me, I shall take care it has justice.

For the second time I protest, in the strongest terms, against your allowing the Magazine to convey garbled statements of things that are quite foreign to the matter at issue; nor do I know of any thing more dishonest than that of quoting part of a statement, when the whole would convey a different meaning. I refer to the experiments I lately made on clairvoyance. A part of a paragraph, containing an account of one of them, was quoted by Mr. Dircks; but, had the whole been given, it would have conveyed a very different impression. As editor, you surely had it in your power to draw your pen through that which had no relation to the matter, more especially when I had remonstrated with you by private letter the first Should I send you time it was alluded to. a paper on the subject, I am sure you would not insert it, and you would be acting consistently with the interests of the Magazine. It therefore being a subject so foreign to your pages, it savoured something of partizanship to give a portion of it, obviously but to wound. I with much respect, THOMAS SPENCER. P.S. I am half inclined to think that from the beginning I have taken this matter up too seriously; the animus of Mr. Dircks must have been very apparent to all, yourself included; and yet, in every communication, you permit him to persist in making statements, and imputing motives, meant to be injurious to myself, and having no other foundation than his bare word. Really, Sir, unless I see at least the semblance of fair play on your part, I must give the matter up in the pages of the Mechanics' Magazine.

am,

T. S.

[We could draw no other conclusion from the manner in which Mr. Dircks treated Mr. Spencer's proposition for a reference to "a competent committee," &c., than that he did reject it, (though not, certainly, in

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express terms,) and Mr. Dircks himself has not disputed the correctness of our conclusion. We are still of opinion that such a mode of proceeding was altogether uncalled for; and though Mr. Spencer may (affect to) wonder at this, we are sure nobody else does. Mr. Spencer finds fault with us for permitting Mr. Dircks to assail him in this way and the other on the strength of his "bare word;" and threatens, "really," that "unless he see at least the semblance of fair play on our part," he must go elsewhere to obtain it. Mr. Spencer will do as he pleases in this respect; but we must distinctly deny that he has the slightest pretext for saying that he has not received fair play at our hands. He has been hit hard through the columns of the Magazine-that is true; but at the same time every opportunity has been promptly afforded to him of defending himself through the same medium-if he could. Mr. Dircks may have latterly diverged a little more from the main points, it is true, than is proper, and have used greater acerbity of language than it is pleasant to observe; but we could not but feel that the unwarrantably disparaging manner in which he was replied to by Mr. Spencer (who could find time for that, though he could not find a moment to bestow on the "stubborn facts" of the case) gave him strong claims to indulgence.-ED. M. M.]

ON THE NEW METHOD OF MEASURING DISTANCES BY MR. HENRY HENNESSY.

Sir,-Although I did not intend to carry on the discussion of a subject which has been already examined, I cannot refrain from making some remarks on the plausible and elaborate dissertation which appears in p. 86 of this volume.

The first objection that "G." brings against my method of measurement, is the great inequality of the sides of the triangles, Ill-conditioned as they may be from that cause, they have some advantages over the triangles of an ordinary survey. They are always right angled. Their other advantages will be easily seen by reference to my paper, (vol. xxxix., p. 276.)

"G." seems to imagine, that in ordinary trigonometrical measurements the sextant, or some similar instrument, capable of being carried under the arm, is used. I have always used the theodolite, and have seldom seen other instruments used for the purpose.

"G." says, (p. 87,) "the adjustment of the portable base to the proper height will, unless an assistant be employed, be an exceedingly tedious, if not impracticable operation." The ordinary method of surveying requires at least one assistant to the sur

veyor, often more than one. "G.'s" objection to my method applies, therefore, to every other.

He further says, that my method cannot be applied to the measurement of inaccessible distances, as determining the width of a river, "unless, indeed, a boat be procured to carry over the portable base." The same difficulty is experienced by an engineer when he meets a river on a line which he is levelling. The levelling staves must be carried across. "G." would not say that levelling is inapplicable to rivers from this cause.

The next objection is, that the method can be used only when the ground is level, or declines from the observer. This objection is extremely futile, as the observer can place himself in any position at the commencement of the line. If the ground does not decline from him at one extremity of the line, it must at the other extremity.

The construction of the proposed instrument next occupies "G.'s" attention. He very properly mentions in a note, that it was unnecessary to make the radius equal to the base, if the only object in so doing was the elimination of the radius from the formula. The real object was, however, to allow the arc to be minutely divided. This equality of the radius with the base is not insisted on, for if in practice it were found to be much weakened by its length, it could be shortened to half the proposed length, still admitting of very minute division on the arc.

There can be no comparison between the proposed instrument and the instruments at the Greenwich Observatory. As the distances measured by the former will probably be never less than 40 feet, the arc (allowing the radius to be 5 feet) will be about 9 inches in length, or nearly the 35th part of the circumference.

The equatorials, mural circles, and other angular instruments used at the Observatory, are complete circles, with radii half as long as that of the proposed instrument, and have arcs seventeen times and a half as great. The well-known maxim of the inverse proportion of size and strength is, therefore, so far entirely in favour of my instrument. Also the effects of expansion and contraction from change of temperature will be seventeen times and a half less than in the instruments to which "G." alludes. By shortening the radius one-half, the errors arising from these causes will be thirty-five times less than in the astronomical instruments. It should be also remembered that the complicated machinery necessary for directing an astronomical instrument to every quarter of the heavens, does not at all accompany this instrument.

When in use the proposed instrument

could be supported similarly to the theodolite, and when not used it could be easily disposed in a properly constructed case, instead of being "lugged about on a man's back, or in some such uncouth mode." From these observations I think I am perfectly justified in considering that "G." has much overrated the probable error in taking the angle of depression for a distance of 500 feet when he assigns it at 5 seconds. His conclusion that there will be an error of 1 foot 2 inches is therefore incorrect.

With distances of between 300 and 400 ft., "G." himself must admit that the error of observation will be practically insignificant. Levelling being the chief use to which this instrument can be applied, as it gives the difference of level and horizontal distance; distances of 400 feet will be seldom, if ever, exceeded. It will be perceived that "G." has not attempted to deny the utility of the instrument in levelling. The time employed in adjusting the common theodolite or level is nearly the same as that which the adjustment of the instrument proposed by me would occupy. But the results given by the latter would be more important, and therefore its use in levelling has not been disputed.

Cork, March 9, 1844.

THE JET QUESTION.

Sir, I would not be tempted to continue a theoretical discussion on the subject of the jet, were it not that I am called on by so intelligent a writer as your correspondent, Mr. Cheverton, to apologize to a third party for a quotation I made, or rather for misconceiving the drift of the experiments made by that party. I cannot bring to my recollection the observation made by Mr. Talbot in describing these experiments, but I have no doubt about having stated accurately the facts, and I believe they had no reference whatever at the time, to the experiments of the jet impinging against a disc, or to that controversy.

Your correspondent thinks there is nothing extraordinary in these experiments, or contrary to what might be expected when the same are manifestly at direct variance with his own mathematical formula. If the latter be erroneous, no doubt the remark might have some weight, and if there be nothing very remarkable, why insinuate their inaccuracy? He should not, however, if he follows the doctrine of Venturi, test the accuracy of philosophical experiments by theoretical inductions. What I contend for is this, if the accuracy of these experiments is to be disputed by your correspondent, they