on so important a subject, when registered in your valuable Magazine, may be converted to some public use -I am induced to send you a sketch and description of it. If it should not be approved, it may suggest some other plan which may be useful.

A, is a mast or pole, of sufficient length to reach over the top of a window, and about the size and strength of the side of a common ladder; or it may be made hollow, of three-quarter deal, to render it lighter and more manageable say 4 inches square at the bottom, and tapered to about 2 inches at the top. This would be so light that two men might run with it upon their shoulders, and strong enough to convey a heavy man from an attic window. It will be observed that a very light mast will be sufficient for this purpose, as the weight of the car and its cargo will be sustained by the cord on the pulley, and press perpendicularly on the top of it; for the lateral weight on the mast will be only what would be necessary to draw a plumb-line from its perpendicular position to its side. Bis a piece of wood or light iron, a little curved, and fastened to the mast to keep it steady at a short distance from the wall. Ca good-sized pulley, say 6 or 7 inches in diameter, to move with ease and little friction, with side pieces to keep the cord in its place. D the car, consisting of two light but strong frames of oak, one each at top and bottom e e; the sides and bottom fff, being of strong sacking, to render it light and flexible for use and convenience in carriage. These frames are united to runners g g, which slide over the mast; hhhh are cords to support the upper frame of the car, and are united at the top to another runner. These cords will form useful handles to assist a person while getting out of a window. The whole of this apparatus is finally fastened to the main cord I, which goes over the pulley.

The superiority of this contrivance consists in the simplicity of its application; for it is no sooner raised against the wall of a house on fire, than it is ready for use; and a man may be hauled up to a window, or lowered from it, in one minute after the mast is brought to the house; and

children or infants may be placed in it and conveyed down, without the least danger; and many cargoes may be saved in a few minutes.

All other contrivances which I have seen described, require some minutes, at least, to prepare, before they can be used. Such, for instance, as throwing up a cord to the person in the room, who must then draw up the principal apparatus, and find some means of fastening it securely to a bed-post or window-frame, &c. All these operations take time, and must be performed by the persons in danger, who are generally too much distracted by their situation, to possess sufficient calmness and presence of mind to attend to the instructions given them by those in the street below; to say nothing of the incompetence of many females or children, to obey any instructions given to them in such a case. But when the Fire Mast is used, a man may be sent up, who can assist a whole family to descend in a few minutes, before any other escapes could be fixed and made ready for the purpose.

I likewise think, that the appearance of this contrivance, when presented at the window, would inspire even a timid female with confidence in the safety of such a conveyance.

Should the plan I now offer to your notice be eventually adopted, I would suggest the propriety of having one in readiness in every street, and of shewing and explaining its use to all the residents, and especially to females. A small subscription by every inhabitant in a street, would defray the expense of all the necessary apparatus, and the mast might be hung up in some convenient entry or passage, as is commonly done with ladders, and the car and cord deposited in some house adjoining; a small sign with Fire Mast painted upon it, might also be placed over the place where it is deposited. I would likewise recommend the inhabitants to avail themselves of its use to convey furniture in or out of the windows of upper rooms, instead of ladders; this would keep the machine in order, and likewise give them some experience in using it. I am, &c.

A. TAYDHILL. Birmingham, June 28, 1829.

The specimen (Fig. 1.) is an ellipsis divided by eccentric and other geometric figures. My apparatus is capable of effecting this, whether the ellipsis be generated by the geometric, or common elliptic chuck, or by any other means that I am at present acquainted with; and it will produce not only any of the figures contained in my former specimens, but others, at the option of the workman, with as much ease and facility as circles.

I have had a dispute in my own mind whether it would be right in me

to shew you a divided ellipsis, after the same thing had been previously done by others, but I assure you I had the method I make use of to invent, not knowing the method of any other person. Besides, Mr. Ibbetson has not said that his method is applicable to the dividing the ellipsis that is generated by the common elliptic chuck; and I believe there are many amateurs, as well as professional turners, who would like to know that an ellipsis so generated may be divided.

The specimen (fig. 2) consists of continued line figures, which any of your correspondents that dispute the originality of my apparatusmay copy if they please; I only hope they will do it to the very letter, for where there is not much, a little is worth contending for. The two inside figures, although they appear detached, are continued motion figures, that is, the tool and block operated on were in continued motion. The outside circle of chainwork is all in one, and but one line, although without very close examination the contrary may appear to be the case. I hope the figures are sufficiently egg-shaped to serve as an answer to Mr. Alexander's query, No. 294, being neither at right angles nor parallel to a radius line. I do not imagine he is so unreasonable as to expect that every egg should be placed in a different position, but even that I could do, though it would require rather a troublesome adjustment for every change of position, and, after all, the effect would be by

no means ornamental.

Now, Mr. Editor, I wish to say a few words to you, before I conclude, concerning the ground of preference you give Mr. Ibbetson's specimens. You say that in the way of turning you never saw any thing that equalled those of Mr. I 's chuck in minute perfection of execution. I suppose you mean small figures on small blocks; if so, I must say this is no criterion of superior excellence in the art, but the reverse, for it is well known to every turner on the lathe, that the more distant from the centre of rotation the tool operates on the work, the more liable it is to vibrate; a difficulty which will more particularly apply in this case, where there is a number of wheels, centres, &c., between the power and resistance. If the figures be large, the errors, if any, will be the more easily detected, and vice versa.

I wish farther to observe, that I have seen a great many very good lathes and their appendages, but they all dwindle down into insignificance when compared with one belonging to Sir Thomas Frankland, of Thirkleby Hall, in this county, which I once had the pleasure to see, and which I may truly say is a master-piece in

turning apparatus. It cost, I was told, nearly £1,100.

I am in possession of both simple and compound geometric chucks, which I constructed shortly after the publication of your 72nd Number, nearly after the plan of the leading article of the said Number, which appears to be in some points superior to Mr. Ibbetson's; for I can generate cycloids and spirals, both circular and elliptic, which Mr. Ibbetson says he cannot. I am likewise in possession of another apparatus, which I made, I believe six years since, which is capable of generating all the curves the simple geometric chuck can generate; and this instrument I sometimes use in combination with the simple chuck, in which case they are in some points more than a match for the double or compound chuck. Now, Sir, with all this apparatus, and the practice I have had in the line, I should be a very dunce if I could not shew you as many hundred specimens as Mr. Ibbetson has done; but when done, there would not be one of them that I could with confidence say was new. I sent you my last specimens, under the impression that they were quite original figures generated by an original apparatus; which impression (after all that has been said and done since) remains as strong as ever. I will not be so absurd as to imagine they cannot be imitated-whatever has been done by one person may be done by another-but Mr. Ibbetson, at least, has not hit the mark, as his specimens in your 291st Number may lead you to imagine; they are quite of a different character, as I can shew, by his own reasoning, if necessary.

Still, in all these lathes that I have seen, there was not any thing that in any way resembled my apparatus; neither have I seen any specimens or figures, that have been printed from either wood, copper, or steel, that in any respect resemble them. I do not include what the apparatus is able to execute in imitation of other machines, such as the geometric chuck, eccentric, fly, or rose engines. In imitation of the rose-engine, I believe its powers to be unlimited, for I have not seen any figure-work that is composed of waved lines, however intricate, but

what it would be able to execute, in the hands of an ingenious and persevering artist.

I am, your's, respectfully, GEORGE CHAPMAN. Whitby, July 13, 1829.

[Mr. Chapman has not understood the words, "minute perfection of execution," exactly in the sense we used them. What we meant to say was, that most of Mr. Ibbetson's specimens are so perfect, that not even the minutest deviation from perfect correctness can be detected in them; and this holds equally true, whether the figures are large or small. The fig. 1, which Mr. Chapman now offers as a specimen of a divided ellipsis furnishes at hand an excellent illustration of our meaning. The division appears at first sight to be perfectly exact, but on a

closer inspection very great inequalities may be perceived. Now, the superiority of Mr. Ibbetson's specimens consists in this, that they will stand any investigation. Mr. Chapman, we should say, divides an ellipsis well, Mr. Child still better, Mr. Ibbetson the best of any.]-ED.

ON THE MEANS OF GENERATING SPIRALS, AND ON COMPOUND GEOMETRIC CHUCKS. BY MR. CHAPMAN.

Sir, I have just received the 78th Part of the Mechanics' Magazine, in which I observe a paper by your correspondent, Mr. Ibbetson, in which he asserts the impossibility of a chuck on a lathe being capable of generating spirals and some other curves, which he names. Now, Sir, I beg to observe, that I am in possession of a simple geometric chuck, and, as I said in a former communication, upon nearly the same plan as the one that is given in your 72nd Number, by which I can generate any of the curves so positively disputed. I will say, for instance, spirals of any number of turns. In fact, the thing is so simple, that it was one of the very first curves which I saw with the eye of my mind, the instrument was capable of generating, before I even took one single step towards the construction of the engine. But as simple assertion is not allowed to have any weight, and even specimens are sometimes termed patched impositions, I will proceed to inform you, and any of your readers that are in possession of a geometric chuck, how the spiral may be generated.

For example-place on the headstock a wheel of 84 teeth (or any other number, at pleasure, to suit the number of turns the spiral is to have); to act in this wheel apply one of 21

teeth on the arbor, and on the opposite end of the arbor place another wheel of 72 teeth, to turn another wheel of 36 teeth, which must be fixed on the principal arbor of the chuck. Now, to generate the spiral, the mandrils of the lathe should only, make half a revolution. To give the mandril a full turn will produce another similar spiral, but the reverse to the former, and the line will return into itself if the wheels be of the above numbers, or any other number that divide properly; which is another property the spiral possesses, though that has been disputed.

The foregoing being properly understood-which I think it will readily be by any one in possession of a compound geometric chuck-he will easily perceive how an elliptical spiral may be generated; and if he is in possession of an apparatus that will divide the ellipsis upon the same principle of the one that I possess, he will also see that the circular spiral may be divided into any number of equal parts. Now, Sir, all this and much more pursuing the same path through all its varieties-may be done, and has been done, notwithstanding all that has been said to the contrary.

In my former papers, as well as in this, I have frequently adverted to the compound or double geometric chuck, but perhaps some of your readers may not have properly understood my meaning. To be more explicit, I wish to observe, that persons who possess a single chuck, and having rung all the changes they can think of by it, may wish for something new in the art, may have this to their heart's content, (if not very unreasonable) by fixing a duplicate or second geometric chuck on the nose of the former, and giving the second motion from the first, in the same manner that the first has its motion from the head stock.

I have been in possession of the above chuck, that is, a compound geometric chuck, a long time; in fact, I made the second a very little while after the first, and the reason that I never gave an explanation of it before, is, because the idea came so easily, and appeared so natural, that I thought the same thing must have

76 occurred to many others as well as myself, and was not therefore worth communicating.

As the above combination, however, has never (as far as I am aware) been yet noticed by any one, either under the name I have given to it, or any other, I presume I may claim the merit (if there be any) of combining two simple epicycloidal chucks (as they are called in the French Manuel du Tourneur, published in 1816, and Mechanics' Magazine, No. 72.) It is no matter if the candle has been burning elsewhere, or how long previous to the date of this communication; it has been under a bushel, and so could not have given any light to me, or any other person. If, therefore, any claim should be set up to priority of invention, it cannot have any weight.

If the above information should be considered of any value by any of your numerous readers, I shall feel great pleasure when I reflect that I have added a trifle to the general stock of amusement and gratification which such pursuits offer, and may probably be encouraged to trouble you with some account of other apparatus at a future time.

Your's, &c.
GEORGE CHAPMAN.

Whitby, Aug. 10, 1829.

HARDENING THIN STEEL PLATES.

To Mr. R. Daniell.

Sir,-In No. 314, of this Magazine, you answered the inquiry of a "Plain Mechanic," respecting the hardening of thin steel plates without warping; and if you can give any information on the following analogous subject, you will oblige many as well as myself.

How are pieces of thin steel (similar to warding-files) hardened without warping them? Or can you tell me the method which file-makers adopt to prevent the warping of their small files in hardening?

If the process is no secret of trade, and you (or any other person) will give it publicity by means of this Magazine, you will confer a lasting obligation on many of the sons of Vulcan.

P. S. F. D. in No. 311, has kindly answered an inquiry of mine respecting the repairing of globes, but if he will insert the address of the maker* he alluded to, and the probable amount of re-covering my globes, I shall feel greatly obliged.

* [In the answer of F.D. as originally communicated to us, the address of the maker, (one William Newton,) was given; but we struck it out for two reasons. First, because the insertion of the address would have been an advertising of the said Newton, and have subjected us to the advertisement duty; and second, because the said Newton is the man who prosecuted a brother journalist (to the death almost), for copying without his leave, certain drawings, which he (Newton) had himself borrowed from that public repository, the Patent office; and is therefore a person whom we have no disposition to oblige, in any way→ not even to the extent of obtaining him an order to renovate a pair of globes. -ED. M. M.]

INDIAN MODE OF CUTTING PRECIOUS

STONES.

Sir, I perused a paper in your valuable Magazine (No. 178, vol. vii.) On the Improvement of the Lathe, and an Inquiry respecting, its Application to the Cutting of Stones." Not having seen it elsewhere, I think a description of the simple mode which the natives of India adopt for the purpose of slitting stones, preparatory to their being polished, may not be unacceptable to some of your readers.

The native lapidaries throughout India are very expert in the process of cutting and polishing pebbles. Having selected the most suitable to their purpose, they slice them, by sawing them with soft and thin iron wire fixed in a bow, leaving at the end a coil to renew the wire as it is worn away by the friction. The workman having seated himself on the ground, drives into it a piece of bamboo about a foot long; in this he makes a slit vertically, to fix the pebble upon which he is to work. He then places an earthen cup of water, and another of coarsely powdered corundum (sometimes only sand), on his left; and having taken the bow in