P. S. From the barometrical observations of 1827 and 28, Epping is found to be 323-9865, or, we may say, 324 feet above high-water in the Thames at Chiswick. But what is the fall from thence to the Nore? Not many feet. Now, High-beech is a few feet below Epping, yet in the trigonometrical survey, under the direction of the Board of Ordnance, this hill is stated to be 790 feet above the level of the sea: I believe it is not more than half so much. The altitudes of the different stations as given in this survey are in general very incorrect.

A well-conducted series of barometrical observations at these and a few other eligible points on the coast, with instruments made as nearly similar as possible, and by the same artist, would be an admirable check to the present results as given in the survey. From others, as well as my own experience with the barometer, I am able to form a tolerable estimate of its value where employed with proper care in this way: it is an interesting and valuable instrument when accurately made.

INDIAN LATHE.

19

T. S.

Mr. Editor, I observe in No. 309 of your Magazine a query, proposed by a Young Turner at Lichfield, who wishes to know how to put a string on a spring-lathe so that the work shall turn continually one way. Now, Mr. Editor, I am not a turner, nor understand the principles of his profession, and I am therefore at a loss for suitable terms to express my sentiments in an intelligible manner; yet if the following information should satisfy his curiosity, I shall feel equal

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ly gratified with himself in being the means of relieving his anxiety. Here I would observe, that I think the friction caused by the string passing round the work will be so great as to render this method of but little use to him in actual business.

The foregoing figure is (from memory) of a model seen some years ago in the Oriental Museum at the East India House; and I believe the maIchine is used in the East Indies for twisting thread and small ropes, and may probably be used by the natives with a spring attached to it for the purpose of a turning-lathe.

The principle consists in passing the string round the work and over a beam or pulley, and then round the work again in a contrary direction to the first time; then by taking hold of one string in each hand, instead of attaching it to the lathe-spring, and moving them up and down, the work or spindle turns continually one way. I am, Sir, Your obedient servant, DAN. GIDSTON.

Newport, Isle of Wight.

IBBETSON'S GEOMETRIC CHUCK. Sir-The various applications I have had respecting the geometric chuck, combined with other circumstances, have induced me to communicate the mechanism of it to Messrs. Holtzapffel, of Charing-cross, who now construct it in its simple or more complicated character for amateurs; and to those amateurs who may purchase it, I am willing to communicate, on the principle of giving lessons, either personally or by letter, that practical information respecting the various adjustments of the different principles of my chuck, which the actual construction of it, and the long experience I have had in working it, enable me to do.

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A CURIOUS SUN-DIAL.

Mr. John Abram, of Canterbury, teacher of the mathematics, and author of the Kentish Tide-tables, has constructed a curious sun-dial, which is to be fixed in the front of the Droithouse, Margate, below the transparent clock. The following are the curious properties of this dial :—On the upper part is the hour-circle, to show the true solar time. Below the hour-circle is the Torrid Zone, on a large scale, with the parallels of the sun's declination (hyperbolic curves), corresponding to every half-hour of the sun's rising and setting; these half-hours are again subdivided into quarters of an hour. The time of the sun's rising and setting for the day is indicated by the extreme point of the shadow of the gnomen traversing the corresponding parallel of declination, which, by its diurnal progress over the surface of the dial, also shows, at any given instant, the true bearing of the sun by the compass, indicated by vertical straight lines, marked with different points of the compass. There are, likewise, other parallels of declination, corresponding to the entrance of the sun into each sign of the zodiac. short, the dial points out the hour of the day, the sun's place in the ecliptic, the time of the sun's rising and setting, the length of the natural day and night, and the sun's true azimuth or bearing by the compass.

First Law. Whatever may be the temperature and pressure under which the steam is produced, the same quantity of heat must be employed to produce the same weight of steam; and as the quantity of heat developed is proportioned to the quantity of fuel, it is obvious that a given weight of steam, a kilograme, for example, will always cost the same price, whether it be produced at a low or a high pressure. This important discovery is due to M. Clements, and is one of the finest results of his numerous investigations.

Second Law.-The volume of the same quantity of steam, is in inverse proportion to the pressure to which it is subjected. This law, discovered by Mariotte, is applicable to all gases. Steam acts, in many respects, as a permanent gas.

Third Law.-The dilatation of steam is of its volume at zero, for each degree of the centigrade thermometer. We are indebted for this law to the remarks of Gay Lussac and Dalton.

Fourth Law.-The latter gives the elastic force of steam, according to the degree of heat at which it is produced. The following table exhibits this law, which can be expressed only by numbers:

2.

THE PHILOSOPHY OF STEAM POWER. (From the Bull. des Sciences.) The following laws of steam were announced by M. Morin, in a course of lectures lately delivered at Ge

neva :--

NOTES ON DR. LARDNER'S LECTURES ON MECHANICS, AT THE LONDON

UNIVERSITY.

(Continued from page 176.)

Thirdly. When several forces are given in any parallel directions, and any others acting in a direction exactly opposite, but all parallel to each other, to find a single force productive of the same effect.

Let AI (fig. 3) represent the plane on which the following given forces, viz. B=6, C=7, D=3, and E=9, act upwards on the points F, G, H, and I, at the several distances from the end A of 5, 6, 16, and 32 inches, and let the downward forces be K=5, L=16, and M 4, acting on the points N, O, and P, at the several distances from the same point A of 8, 18, and 20 inches. Now it is evident there are

LA M

16

still two conditions to be observed: 1st. Whether the sum of the upward be equal to that of the downward weights, (which may be found by addition,) for were the weights alone to be considered, they would be in equilibrium. 2nd. Whether the weights act in their proper places, which is to be found by the same rule as before; thus taking the upward forces.

L M

And since they are in equilibrium they destroy the effects of each other, and the plane will be at rest.

There is one more case to be attended to. Fig. 4.

Let AD (fig. 4) represent a plane, on which act the two unequal forces or weights C and E, in opposite directions, and of which E is the greater.

It is required to find the place and weight of a single force that will produce equilibrium. Now from what has been previously stated, the required force will be equal to the difference of those which are given, viz. E—C. With regard to its place, it has been shown that two forces will keep a single force in equilibrium if one force bear the same proportion to the other, as the distance between the opposite weight and the single weight. Now supposing the distance between the points A and B to be expressed by the letter e, this proportion will stand thus ~(E—C)·.·C::e: the distance between the point B and that on which the weight (E-C) acts, and which distance may be called d. But if the weights C and E be known, then the other parts may be also discovered (provided the distance between them be also given). Let the weights C=3

the boat: but in passing from the inferior to the superior canal, powerful engines are required. These consist of capstans, from which ropes are passed round the stern of the boat. The effort of a hundred men is sometimes required to effect the elevation of a loaded boat. The objection to this mode, taken in this simple and rude form, lies not only in the great labour required by it, but in the injury which must necessarily be done to the boats. The practice could never be adopted with the slightly-timbered barges used in our canals, which are calculated to be supported by the fluid in which they move, and which presses with a force perfectly equal on every part with which it is in contact. There are some situations, however, where, from a scarcity of water, the inclined plane is necessarily substituted for the lock. Some works of this kind are used on the Continent of Europe; and in England, in some cases where the weight of the descending greatly exceeds that of the ascending commodities-as in the traffic between mines and 'furnaces-inclined planes are used with advantage. In these situations, the descending and loaded boat is made to drag up an ascending one, which is empty, or but lightly loaded; thus exhausting in a useful purpose a force which not being expended in friction, as rollers or wheels are used between the boat and the plane, could not be otherwise controlled without some labour and cost.

MINOR CORRESPONDENCE. Jackson's Patent Studded Shoes.-Sir, My master, who takes in your valuable Magazine, having told me what he had read in it about Jackson's Patent Studded Shoes, I bought a pair of them, upwards of two months ago, which I have worn ever since in my humble occupation of a bricklayer's labourer, and find them as yet scarcely the worse for wear. On telling my master how much I was obliged to him for the information, he said the least I could do was to thank you, from whom he had it; and this, as in duty bound, I now do. I generally wore out a pair of nailed shoes in about three months, but I think the studded shoes will last me twice as long. I was rather afraid the studs would catch the rounds of the ladder, as the common nails often do when they are sometimes drawn out; but I do not find this to be the case with the studs. Sir, your obliged servant,

P. O. B. The Railway System.-Sir, In the Morning Chronicle of the. 1st of last month there is the following paragraph respecting the Ohio Rail

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way: "The entire line of the railway is in steady progress to completion, with as much order as any undertaking of similar magnitude can be conducted." Ohio is, as your readers are aware, one of the back states; and as railways are already laid down throughout the United States, your readers have to complain not that you are arousing the public to this subject, but that the United States have taken the lead. Your correspondent "B" will perceive that you are labouring to prevent the United States from wresting from us our commercial and (I may add) maritime superiority, and that Liverpool and Manchester are but acting in self-defence.

Nov. 2.

I am, Sir, your obliged servant,

T.

Railways.-Mr. Editor, With respect to the proposition of "W. B." in your Magazine of Oct. 24, 1829, No. 324, relative to the putting "rollers" in the place of the surfaces that the locomotive carriages now go on, I should like to offer you some particulars in furtherance of his scheme, but that would be useless, until it is ascertained by what contrivance those rollers

are to be put in motion. "W. B." seems to

have overlooked that the motion of the machine is dependent on the wheels of it, impelled by the power of the materials within it; and that deprived of its own wheels, and their moversteam-the machine must stand still. However, where horses are used, I think his scheme worthy a thought, and that all difficulties would be removed. I should be glad to see this noticed by some competent practitioner of experience in your Magazine. I am, Sir, yours, &c.

C. H.

Sir, Although I take a lively interest in railways and railway carriages, and am by no means of the opinion of your correspondent "B," yet I do not see how the wheels in any of the carriages are propelled; and if you will be so good as explain how the wheels of "The Novelty" are put in motion, you will greatly oblige, A YOUNG READER.

(If our " Young Reader" will study a little more attentively the engraving on our 130th page, and imagine to himself what will be the effect on the bell-crank E, and connecting rod D, of alternately moving upwards and downwards the sling F, he can scarcely miss perceiv ing that that effect must be to turn the wheels continually round. This is commonly known by the name of the simple crank movement, and was first devised by Watt.-EDIT.]

Sir, Some time back I invented a pendulum, which oscillates in a cycloid. I believe rewards have been offered for a pendulum of this description, because some great advantage would accrue to the astronomer, from the equable motion which mathematicians say must result from its describing a cycloid. Any gentleman informing me what the rewards are, by whom they are offered, and how they may be obtained, would confer a benefit where it is needed.

INDIGENS.

[We are not aware that any reward has been specifically offered for such a pendulum as our Correspondent states he has invented; but it being one of the peculiarities of the cycloidal curve, that a pendulum wheel oscillating in it must perform all its vibrations in equal spaces of time, such a pendulum would supply so obvious a desideratum, in the measurement of time and determination of the longitude, that the inventor could scarcely fail to reap an ample reward by the disclosure of his invention.We take it for granted that our Correspondent is aware of the cycloidal pendulums invented by Huygens and De la Hire, and that his invention is something more perfect than either. EDIT]