rotary motion being now communicated to the under roller D from the cog wheel and pinion G and H, the endless band of butts is made to revolve, and as each butt rises from the pit, and passes between the rollers D and E the partially or wholly exhausted liquor is pressed or squeezed out of it by the weighted roller, so that it descends again into the pit with its pores open for the reception of a fresh supply of tanning liquor. A boy attends to the endless band as it emerges from the pit (as shewn in fig 2,) to lay each butt smooth and even upon the under roller D; and it is found in practice that one boy can readily attend to two adjoining pits and pairs of rollers at a time. The pits the patentees have hitherto used are of the ordinary size and form, but they recommend that they should be made at bottom of a semi-cylindrical form, to allow of the endless band of butts turning round with greater ease.

MESSRS. HERAPATH AND COX'S NEW TANNING PROCESS-REPLY OF MR.

HERAPATH TO MR. CHAPLIN.

Sir, I assure Mr. Chaplin (p. 353) that I have no wish to establish my patent upon the ruin or injury of any other. I am so frequently appealed to in cases of manufactural difficulties, and have seen such vast sums thrown away from a want of chemical first principles, that I am sometimes induced to give an opinion before it is asked; for doing so in this instance, I have to apologize, as Mr. Chaplin must be the best judge of his own affairs, and my only anxiety will be to explain those parts of my communication which have been thought inconsistent.

A solution for tanning upon entering the pores of the skin, is quickly deprived of its tanning and extractive matter, but the exhausted fluid remains within the tubes of a wet hide for weeks or months, being only slowly removed by the principle of exosmosis, or partially so by the operation of "handling." The desideratum of tanners has long been to find a cheap and quick method of getting rid of this exhausted ooze, and replacing it with a stronger solution. There is no difficulty in filling those tubes when the

hide has been dried, because then it is effected by capillary attraction. Mr. Chaplin will see then that it is possible that tanning liquor passing through a hide may tan the sides of the tubes through which it passes to the other surface and may fill for once the arteries and veins through which there is no current; but as the liquid cannot be renewed in the latter, the exhausted ooze remains in them until the apparently tanned hide is dry; when upon being introduced into water, the veins and arteries being untanned are immediately filled with water, and the leather is pervious. There is therefore no inconsistency in my statement. The eye is not a sufficient judge of the completion of the tanning process where part of the pores only have been tanned, because the distances between the tanned and untanned pores are only microscopic.

Mr. Chaplin states that the white slimy substance which oozes through the skin cannot be gelatine, because it tastes bitter and precipitates gelatine,and kindly offers me a means of satisfying myself that it is only tannin. I feel obliged, but have already analysed a portion of the white matter from a sample of the leather, and found it to be a compound of tannin, gelatine, and lime, and if that gentleman will make two more simple experiments, he will satisfy himself that I am right. First let him heat a bit on platinum foil or a glass plate; it will melt, then char, and will give off the well known smell of burning animal matter, which would not be produced were it only tannin, and he will find the ashes to be lime, which he may prove by a bit of moistened turmeric paper.

If the increased weight of my leather was owing to artificial or extraneous additions, itwould be dishonest to take advantage of the ignorant trader by selling it as leather; but it is not so: I retain the gelatine in the hide by preventing its being dissolved in the oozes; I tan the retained gelatine by giving it its due proportion of tannin and extractive, and thus increase the real matter of the leather, and consequently its durability, and its impermeability to water. It may be said that the shoemaker will lose by paying a halfpenny a pair more for his soles, but he will have more profits from customers who will have found the bene

fits of dry feet, and the economy of wearing shoes which have not required constant mending.

I perfectly agree that weight alone is not a sufficient test of the value of leather, nor have I advanced such an idea the sentence ran thus: "I will engage to use his own liquors, whether from bark, valonia, divi divi, or terra japonica, and to return him 3 lb. per hide more than he can make by the ordinary mode."

Mr. Chaplin has misunderstood me when he believes me to object to the system of transfusion, merely because it was a quick process." If the sentence is read as a whole, beginning after the word "weight," it will be seen that other circumstances besides quickness are given as reasons for the deficiency of weight and the permeability of leather tanned by transfusion.

In the course of a few days my specification will be enrolled, when the public will decide whether the new plan be or not a simple and philosophical means of surmounting the difficulties which the tanner has hitherto experienced. In the mean time I invite examination and trial of the few samples sent into the London market (which have been deficient in colour, however, not as a necessary consequence of the process, but from the difficulties attendant upon first experiments) and shall feel pleasure in answering any objections which may be urged with the urbanity and intelligence displayed by my present opponent. Yours, &c.

WILLIAM HERAPATH. Bristol, March 1, 1838.

THE CONTROVERSY BETWEEN NAUTILUS, O. N., &c.

Sir, I have sometimes been inclined to think that your able mathematical correspondent, Ó. N., in his first lucubrations in the Mechanics' Magazine was acting the character of the "Dougal creature" in Sir Walter Scott's historical novel of "Rob Roy ;" and I am pretty sure Nautilus has by this time discovered that he very much underrated his scientific attainments when he reproved Kinclaven for condescending to notice some of his first essays in the

66

Mechanics' Magazine. But be that as it may, my present purpose is to make some remarks on Nautilus' last, and I must also say very intemperate, letter (763) inserted in your minor correspondence In the first place I must in form Nautilus, that at the time I wrote my last letter (761) I had not seen his (758) and I will also farther inform him, that even if I had seen it I certainly would have taken no notice of it. The task I was called upon to perform was to answer a question put to me by O. N. (755). namely, "whether he, O. N., had mistaken my meaning in the answer he gave to my question" (743), which was why the perpendicular P N must fall upon D Z' produced, the latitude of the places of observation being 55..58 N." The answer O. N. gave to this question was, "if the perpendicular P N did not fall upon D Z' produced, then by a very simple calculation it might be shown that the zenith distance of Procyon would be greater than 90° &c." This was a simple and proper answer; in fact it was the only true answer that could be given to my question. And further, in justice to O. N. I must also state that the answer he gave to my second question which he deduced from the principles he so ably demonstrated in his letter (732) was equally judicious, and I trust, Mr. Editor, you will believe me, when I say, that had O. N. given an improper answer to either of my questions I would have lost no time in telling him so. But right or wrong Nautilus appears to have been determined to find O. N. in error, on my first question. Accordingly, in No. 751, he makes the following most illiberal remarks::

"O. N. has made another unfortunate slip, when he says in answer to Iver McIver's question of 'why the perpendicular P N must fall upon D Z' produced,' that if it did not, the zenith distance of Procyon would be greater than 90°."

This was the passage that O. N. called on me for my opinion upon (755) and this I gave; and I can with truth aver, in the most impartial way I could devise (761). Nautilus in continuation says, 66 now a slight consideration of the particulars before given will show that from a to b the perpendicular P N must fall inside of the triangle, and not upon DZ' produced, and yet that the zenith distance

of Procyon is less than 90° since it has already risen. It is not till after b that it becomes necessary to produce D Z'".

No one can be so dull, as not to see at once that the latter part of the above quoted observations, as well as the first, was intended for the direct purpose of proving that O. N. was in error in the answer he gave to my question, and I must say, that a more disengenuous mode of going to work I have never seen (and I hope I shall never see again,) used by any of the scientific writers in the Mechanics' Magazine. Now what is the truth? Why simply this, that all these observations of Nautilus only hold true within the limits of the two latitudes 57..59.10 N, and 57 .. 22..32 N. Now in O. N.'s solution of his own question, the lat. of the place was not within these limits, as it happened to be 55..58 N. So that Nautilus in his vain attempts to prove that O. N. was in error has been under the sad necessity of contradicting himself. This is really too bad.

Had Nautilus attended to the general principles demonstrated by O. N. (732), he would have discovered that all the information which he fancies he has given us (751), are only simple deductions, which necessarily follow from O. N.'s premises; the only thing new that I can discover, is in giving the lesser latitude 57.. 22.. 32, and this is found at once by calculating P Z on the supposition that D Z' is 90°.

But in the teeth of all this, Nautilus, in his last letter, now pretends to say, "that in the latitude of Edinburgh he had never denied that the perpendicular PN must fall upon DZ' produced," and this information he gave a week previously to the date of my last letter. Well, suppose I should be inclined to admit this (which I do not) to be true, then I would insist upon Nautilus telling us what slips ON in reference to my question had really made, and this Nautilus might have found would have been only leaping out of the frying pan into the fire.

In making the above remarks, Mr. Editor, I have been obliged to associate O. N. with myself, for this plain reason, that had he been wrong I must have been so too. O. N., I see from his last letter (761), intends to reply to that of Nautilus (758); he may do so, although I should imagine that both gentlemen

have already nearly exhausted all the information they can give us on that subject.

I am, Mr. Editor, yours, &c.
IVER MCIVER.

PATENT WARMING-PAN.

Sir,-Some time ago, Col. Maceroni in one of his ordinary de omnibus rebus communications, mentioned that in 1814 he had caused to be made by an ironmonger in Bishopgate-street, a warming-pan, which was to be heated by containing hot water. One would have thought that this would have been the natural gradation from the more primitive plan of warming a bed with a bottle of boiling water: but not so, the simplest plans, sometimes leading to the grandest results, are often overlooked. This was evidently the case with our forefathers in the instance now under consideration; they skipped from the hot-water bottle to the burning-coal pan, leaving the honour of the invention of the hot-water warming-pan to the present enlightened generation.

Col. M. does not appear to have been aware that the invention which he thought of so little importance as to throw out as a mere hint for the benefit of a thankless public, had been the subject of a patent. Such, however, is the fact; for, be it known, that on the 24th of May 1834, his late Majesty's royal letters patent were granted to Stephen Hawkins, of Milton House, in the county of Hampshire, gentleman, for "certain improvements in warming-pans or apparatus for warming beds and other purposes." It should be observed that this grand discovery was made by a gentleman, enjoying probably the otium cum dignitate, warm in the pursuit of science, ardent in his researches into the economy of nature. It is most likely the invention was the result of much study, and that it was not a mere discovery, fallen upon by chance. Mr. Hawkins, is therefore, deserving of the greater honour. From the specification enrolled in his Majesty's High Court of Chancery, pursuant to the proviso in the patent, I have taken the following particulars of this invention. The patentee proposes that a pan should be made of copper or other suitable metal, and which he represents in an accompanying drawing as

Sir, In the 764th number of your Magazine, you were obliging enough to notice a little pamphlet of mine containing a life of Sir Samuel Morland: I send you a description of one of his speaking trumpets in Trinity College library thinking it may prove interesting to some of your readers.

It consists of a large hollow copper trumpet six feet long, the diameter of the lesser end being 14 inches, and the diameter of the larger end 1 foot 3 inches. It is unfortunately much bent at the larger end.

was

If any one have the curiosity to inspect this trumpet, which is perhaps the only original one now in esse, I would advise him not to try its effect in magnifying the voice: on me it had quite a contrary effect, for mouth my instantly filled with dust, and I was hoarse for some time afterwards. As far, however, as carrying" the voice is concerned it succeeds excellently, for it carried mine quite away.

Your obedient servant,

have resorted to, is that recommended by Col. Maceroni at page 299 of your last volume, which I have no hesitation in saying is the very best I have met with, and I take this opportunity of returning thanks for the information. I happen to know, that many other persons have availed themselves of the publication of this simple but valuable recipe. I have not attempted to meddle with the "wax polish," and find that some of those who have tried it have not been successful. The plan I follow in applying this, or any similar composition, is first, thoroughly to clean the boots, to black and polish them as highly as possible and then lay on the composition as directed. By this means a good black colour is insured from the first, and in the course of a blacking or two afterwards, the boots will carry a pretty good polish.

There is one caution necessary to be given, which is, not to apply the tallow and rosin dressing to tight boots; for in consequence of the powerful frictionmaking properties of the rosin, it is next to impossible to get boots that are in any way tight, off or on, after being prepared with this composition. The adhesion occasioned, is such as to set patience, perseverance, and boot-powder at utter defiance. There are some situations where a knowledge of this property may be turned to good account-the belting of mills for instance. There is a valuable and interesting paper on this subject in your last number, in which the writer, Mr. I. H. Beard, recommends that the belts should be stuffed with bees-wax and tallow. The tallow and rosin will be found infinitely superior for this purpose; for besides the preserving properties of this preparation, the firm hold upon the drums given to the belts, will permit them to be so slack as to run very free and easy, and yet most effectually prevent slipping. As a dressing for leather previous to making up into engine-hose, &c., Col. Maceroni's composition is preferable to all others. It is a common practice to prepare such leather by well oiling it; the oil lies in the pores of the leather, whence it is is driven out the very first time the hose used under pressure, forming a scum on the outer surface. The composition, when cold, forming a tenacious sub

stance, gives a greater body to the leather, fills up more effectually and 'durably the minute interstices of the skin, and renders it water-tight from the first.

Two months is, perhaps, an early period, to give any decided opinion as as to the preservative effects of this composition when applied to leather; but the present appearances, together with my previous knowledge of the subject, leave no doubt in my mind of the correctness of Col. Maceroni's statements respecting it.

I remain, Sir,
Your's respectfully,

London, April 4, 1838.

WM. BADDELEY.

INVENTION OF THE CAMERA OBSCURA.

Jo.

Sir,-The camera obscura is now so well known, but still considered so curious and amusing, that some account of its early introduction may perhaps not be uninteresting. The invention of it has been claimed by two or three persons; it was ascribed by Vasari, to Leon Baptista Alberti, a celebrated architect of the 15th century, but there are the strongest grounds for attributing it to John Baptista Porta, who was born A.D. 1445, and was a Neapolitan; since he gives a very minute detail of it in his book entitled, "Magia naturalis, sive de miraculis rerum naturalium, libri 20. Baptista Porta auctore"-Speaking of the various effects of concave glasses he says—“ Before I have done speaking about the operations of this glass, I will tell you a use of it, which is very amusing and ingenious, and by which we may observe many curious natural phenomena; it is to see all things in the dark that are done outside in the sun, in their true colours. First, the room must be thoroughly darkened by closing up all the windows and crevices for if there be any light in the apartment, the effect of the experiment will be entirely spoiled. Make a hole, the breath and length of a person's hand; above this, place a little leaden or brass table and cover it with a thin coating of glue; make a round hole in the middle of it the size of a finger; opposite this let there be a wall of white paper or white linen, and by this means you will see all that is done

outside in the sun, those that walk in the streets like your antipodes; whatever is on the right will be seen on the left; all things will have changed their direction, and the further they are from the hole, the larger will they appear. If you bring your paper or white table nearer, they will look smaller, and more distinct, but you must wait a little, for strong similitudes sometimes cause affections in the sense, which are often so great that they trouble the organs not only while the senses are acting but after they have ceased acting. For instance, if we walk in the sun, and then suddenly go into the shade, the sensation continues, so that we can hardly see, because the affection made by the light is still in our eyes, and when that is gone, we are then able to see clearly in shadowy places. I now mention what I have hitherto concealed, and what I had some thoughts of never revealing-if you put a small centicular crystal glass to the hole, you will perceive all the figures much clearer, the countenances of people walking, &c."

The description here quoted is certainly sufficient to establish Porta's claim to the invention, since it appears that he speaks as if he had not the least idea of its being ever attempted before, and reveals it as something not previously known. It is very probable that the part of Leon Alberti's book on architecture referred to by Vasari, alludes only to an instrument for reducing drawings or views to smaller sizes, in their proper colours. Porta's description, however, is so exceedingly exact, that it is impossible to mistake the instrument he ineans, which answers precisely to the camera obscura now in use, having been materially improved by Gravesande, the Dutch philosopher. Your's, &c.

J. C. W.

MESSRS. SEAWARD'S PATENT SLIDE

VALVES.

Sir,-In your last number, for April 7th, I observe that Mr. Francis Humphrey lays claim to a priority of invention for the slide valves, which I have patented and used successfully these four years, without ever having had my claim for a moment disputed: he says that in the year 1832 he made a drawing which was