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TEMPORARY FIRE-ESCAPES.

Sir,—Much as has been said upon the subject of fire-escapes, it occurs to me that there is still much remaining to be done, before choice can be made of any method, as superior to all others; for if a particular plan be not adopted, constant confusion must be the consequence of a multiplicity of these inventions.

Fire-escapes may be distinguished into two kinds,-one including such as may be supplied by the furniture of a chamber, or any of the portable escapes procured by the sufferer; and the second, those which are not intended for keeping in houses, and consisting of ladders, elevators, and other machinery, brought to the spot by the populace. The first kind are frequently too scanty to afford relief, or the individual does not, under the trying circumstances of the moment, possess presence of mind sufficient to descend by the assistance of clothes, beds, or ropes. Then, again, the second sort are seldom so near at hand as to be procured within the requisite time. Persons may be stifled by the dense smoke, or driven from the windows by the falling of the floor, even before the machines are sent for. The only remedy for these evils would be for every house to be provided with temporary fire-escapes. This, at first, may appear a strange proposal, as well as an incomplete one; but it is, in fact, quite the reverse: and without something of this nature, every kind of machine intended for elevation from the street, must, in a majority of cases, be perfectly useless. To make this clearer, we will only instance a fire commencing in the night time, on the ground floor of a lofty edifice. When the calamitous event is discovered, not only is time lost in procuring fireladders, &c., but, in the absence of those who have gone for them, the entrance to the building is forced open, the fire rages with increased vigour, and the inmates are no sooner acquainted with the danger of their situation, than, without waiting for assistance, they either jump from the windows, or try to

escape by the stairs; and in either case, the most fatal effects are the result.

To provide for the timidity of those who would be fearful of dropping or lowering themselves from the upper stories of a house, as also to give efficacy to ladders, &c., I consider that the temporary fireescape I have now to describe would prove highly beneficial, Being manageable by any single individual, it affords an instantaneous means of remaining suspended outside the window, until the arrival of machinery for making an effectual escape. Besides, not only would the situation of the person be evident, but that time, which at present is always wanting, would be gained, for proceeding properly to work in, recovering the inmates of the house. And in all cases where children are to be saved from the fire, this means of doing so would be certain. In this particular, it has an undeniable advantage over any other fire-escape.

Fig. 1, the escape, hanging outside a window. It is made of strong sail canvas, in the form of a bag or basket, with the rim distended by an iron frame, having joints at the four corners, making it moveable, like a parallel rule. The bag is attached, by four short chains, to a metal bar with bolts at both ends, to lengthen it according to the width of the window.

Fig. 2. A, the metal bar; b b two bolts; c c the four chains, holding the bag D D E. As the two longest rods of the frame DD can be brought close together, this apparatus, when rolled up, occupies but little space.

Fig. 3. This simple apparatus is merely intended for a chair; and the engraving shows how it may be used for making a chair serve as a stand for one person. A are two short, and B two long ropes, tied together at C; and have four loops at D, to receive the legs of a chair. AC are the chain and hook, for fastening it to the window-frame. I am, Sir, yours, &c. HENRY DFinsbury, May, 1829.

HINTS IN ARITHMETIC. It will greatly facilitate the reduction of fractions,-by far the most important part of arithmetic, -to extend the Multiplication Table to the 9th product of all numbers less than 21; the products of 11 with 13, 17, 19; of 13 with 17, 19; of 17 with 19.

To multiply by any number from 100 to 120, in one line, multiply by the two right hand figures twice, and to every after product with them, add the back figure, omitting one place of figures. Lastly, bring down the two left hand figures of the multiplicand.

For multipliers not exceeding 20 +, or -100, multiply by that difference, setting the product two places to the right. Add or subtract, as the multiplier is more or less than 100.

For multipliers ending in 9, use the next number in 0. Subtract

the unit multiplicand from the unit multiplier. Carry one to the place of tens, as in common subtraction. From every product figure subtract the next left hand figure in the multiplicand.

For multipliers ending in 1, use the next number in 0. Take the sum of the units. To every product add the next left hand figure in the multiplicand.

A few examples and observations

Example.-Cwt.

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will show the advantages of decimal

arithmetic.

It is the same thing whether we divide by 5, or multiply by (2); the same of their like powers. Let the price be always expressed in duced. If the price contains farPractice, by a vulgar fraction rethings, the first denominator will be 960.

let it be a decimal fraction, and vaWhen the quotient is fractional, lue the answer as follows:-Take for the shillings, dividing by 5. Then reckon what is over, prefixed to the next figure, as so many farthings minus I, when the farthings

are 25 or more.

=,5416';=,7083; 2,7916;

9583; 02081;=,10416;

,14583.;,22016;=,27083; 1,35416; 1,39583; 2347916;

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carried on successfully to its termi nation. Both these plans I now take leave to transmit to you; and request, that if they should be deemed worthy of notice, you will have the goodness to let them appear in your valuable Miscellany. I am, Sir, Yours, &c.

M. H.

I. Plan for protecting the Tunnel while in the course of Excavation.

A number of rafters, of a sufficient length to have extended from six to ten feet, on each side, beyond the breadth of the intended excavation, were to have been covered with plank, so as to form a floor, rendered water-tight by caulking, or by being covered with tarpaulins. The breadth of the proposed bottom, or shield, might have been from twenty to forty feet, more or less, as might have been deemed most convenient; and when finished, it would have been sunk immediately over the entrance of the Tunnel, 'under the river, and have been weighed and advanced in proportion as the work advanced. The materials employed in constructing the proposed bottom, or roof, might have been very light, from the mode in which it was proposed to carry on the excavation; which was as follows:-Instead of opening the Tunnel to its full breadth at once, it would have been divided into seven equal parts, and each alternate part only to be opened at first, leaving the three intermediate parts as piers to support the roof; and after the four first excavations had been carried as near as might have been deemed safe, to the outer edge of the artificial bottom, wooden props would have been placed for its support, and the piers removed, and the arch of the Tunnel so far completed; when the artificial bottom would have been weighed, and advanced as far as its breadth beyond the arch. And in that manner the Tunnel might have been carried on with perfect safety, and at much less expense, as it would not have been necessary to have sunk it so far below the bed of the river.

II. Means by which it is supposed the Tunnel may still be carried on, and completed with safety.

Let a vessel be constructed, in the form of a chest, or coffer, about six feet deep, and of a length sufficient to extend about six or eight feet beyond the Tunnel, on each side, and at any breadth that might be deemed most convenient,-the top as well as the bottom to be made water-tight; and it must be surrounded by boards an inch thick, placed perpendicularly, their ends projecting below the bottom of the coffer a foot or more, ac

cording to the depth of the mud into which they are intended to enter. Being then loaded with a weight deemed sufficient for fixing it pro perly in the desired position, and the hatch properly closed, it may be sunk by letting in water through a scuttle, which may, when necessary, be closed, and the vessel pumped out, although under water; when it may be raised with great facility, and then advanced in proportion as the Tunnel is advanced; which might thus be carried on with perfect safety, to its completion.¡

SLIDE OF ALPNACH.

[An esteemed correspondent has favoured us with the following ac. count of the celebrated Slide of Alpnach, which, he justly observes, presents one of the most remarkable practical exemplifications on record, of the principle of accelera. ting velocity, treated of by Mr. Mackinnon in our last Number, pp. 270, 271. It is extracted from an account, which was communicated by Professor Pictet, of Geneva, to Dr. Brewster.-EDIT.]

For many centuries the rugged flanks and the deep gorges of Mount Pilatus were covered with impene. trable forests. Lofty precipices encircled them on all sides. Even the daring hunters were scarcely able to reach them, and the inhabitants of the valley had never conceived the idea of disturbing them with the axe. These immense forests were, therefore, permitted to grow and to

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perish, without being of the least utility to man, till a foreigner, conducted into their wild recesses in the pursuit of chamois, was struck with wonder at the sight, and directed the attention of several Swiss gentlemen to the extent and superiority of the timber. The most intelligent and skilful individuals, however, considered it quite impractiinaccessible stores. It was not till cable to avail themselves of such November, 1816, that M. Rupp, and three Swiss gentlemen, entertaining more sanguine hopes, drew up a plan of a slide, founded on trigono. metrical measurements. Having purchased a certain extent of the forests from the commune of Alpnach for 6000 crowns, they began the construction of the slide, and completed it in the spring of 1818.*

The Slide of Alpnach is formed entirely of about 25,000 large pine trees, deprived of their bark, and united together in a very ingenious manner, without the aid of iron. It occupied about 160 workmen during eighteen months, and cost nearly 100,000 francs, or £4250.

It is about 3, leagues, or 44,000 English feet long, and terminates in the Lake of Lucerne. It has the

form of a trough, about 6 feet broad, and from 3 to 6 feet deep. Its bot tom is formed of three trees, the middle one of which has a groove cut out, in the direction of its length, for receiving small rills of water, which are conducted into it from various places for the purpose of diminishing the friction. The whole of the slide is sustained by 2000 sup. ports, and in many places it is attached, in a very ingenious manner, to the rugged precipices of granite.

The direction of the slide is some. times straight, and sometimes zigzag, with an inclination of from 10° to 18°. It is often carried along the sides of hills and the flanks of precipitous rocks, and sometimes passes over their summits. Occasionally it goes under ground, and at other times it is conducted over

These dates must be erroneous, as Mr. Playfair saw the slide in operation in 1816.-Ed, Mech. Mag.