in respect to importance?—They are to be compared, and one is to be placed against the other. The view that I have taken all along in laying out railroads has been rather to go round than to go over high ground.

You find by experience that that is the most convenient?—Yes. As velocity is so easily commanded by a railroad, small detours are not to be compared with the expense of going over high ground? Of course there is a limit to that; but usually a level through a circuitous course is better than an undulating direct one.

Finding that the unequal grounds of the South Downs are interposed in the direct line between London and Brighton, have you been led to take somewhat of a detour by the Valley of the Adur rather than encounter the difficulties of the high ground?Decidedly; and there is no other gap in this ridge of hills but in the line which I have taken.

In an engineering point of view, have you any doubt whatever but that is the best course to adopt?-I have not the smallest doubt of it.

Have you any doubt, in going round by the Adur, of preferring that to that line which would go over the higher ground?—I have no doubt in the present instance.

REVIEW OF RAILWAY BOOKS.

"The Practical Mechanic's Pocket Guide," by R. Wallace. [Continued from p. 228.]

IN the single acting engine, the loss of motive force due to the same causes is 402 of the pressure of one atmosphere: hence, the effective pressure is 598 of this pressure. To determine the mean effective pressure, when the force of the steam in the boiler is different from that of the atmosphere, multiply the given pressure in inches of mercury by 598, and from the product subtract the pressure due to temperature of the uncondensed steam, the remainder is the pressure required, in inches of mercury; multiply this pressure by 14 lbs., the atmospheric pressure on a square inch, and divide the product by 30, the quotient is the mean effective pressure on a square inch of the piston, which, multiplied by 7854, gives the pressure per

circular inch.

In the double acting engine, the loss of motive force due to causes above mentioned, is estimated by Mr. Tredgold at 368 of the pressure of one atmosphere, hence the effective pressure is 632 of this pressure; consequently, the mean effective pressure on the piston, when the force of the steam in the boiler is different from that of the atmosphere, is found by the rule in the preceding article. The force of low pressure steam in the boiler is generally equivalent to that of 35 inches of mercury, the temperature being

220°; and the temperature of the uncondensed steam 120°, its force being equivalent to that of 3.7 inches. Hence for the single engine, we have 35 × •598 = 20′93 inches, and 20·93−3·7 = 17·23 inches; whence 17.23 × 14.75 = 254·1425, and 254·1425 ÷ 30 = 8.47.142 lbs. nearly, per square inch; consequently 8.47142 × •7854 = 6·66 lbs. nearly, per circular inch. For the double engine we have 35 × •632 = 22·12 inches, and 22·12 −3·7 = 18.42 inches; whence 18.42 × 14·75 = 271.695, and 271·695 ÷ 30 = 9.0565 lbs. per square inch; consequently 9.0565 × 7854 = 7.1 lbs. per circular inch.

To calculate the Power of a Steam Engine.-The common atmospheric engine.-Multiply 5.9 times the square of the diameter of the cylinder in inches by half the velocity of the piston in feet per minute, and the product is the effective power in lbs. raised 1 foot high per minute. Divide this product by 33,000, and the quotient is the number of horses' power. 2d. The atmospheric engine with condenser. Apply the above rule, but instead of 5·9, use 6 for the multiplier. 3d. Single acting engine. Multiply the mean effective pressure on the piston by the square of its diameter in inches, and by half the velocity in feet per minute, and the product is the effective power in lbs. raised one foot high per minute. The number of horses' power is found as above. 4th. Double acting engine. Apply the preceding rule, but instead of half the velocity use the whole of it for a multiplier.

To calculate the Power of an Engine when the Steam acts Expansively.-1. In the single acting engine.-Multiply 2-3 times the common logarithm of the reciprocal of the fraction, denoting the portion of the stroke made when the steam is cut off, and to the produce add 3; then multiply the sum by that fraction, and by the whole force of the steam in the boiler, in lbs. per circular inch; the product is the mean effective pressure on the piston, with which proceed as directed in the double acting engine. Divide 2-3 times the common logarithm of the reciprocal of the fraction, denoting the portion of the stroke made when the steam is cut off by the reciprocal itself, and multiply the quotient by the whole force of the steam in the boiler, in lbs. per circular inch; the product is the mean effective pressure on the piston, with which proceed as directed in the preceding paragraph.

"A Treatise upon Elemental Locomotion," by Alex. Gordon, C.E. MR. ALEXANDER GORDON, C.E., has just published a work under the above title, the object of which is to advocate the application of steam carriages on common roads in preference to railroads. Mr. Gordon writes like a man well acquainted with the subject he writes on, and warm in the side he takes. He has advanced some circumstances which certainly deserve our serious consideration. We are prejudiced in favour of railroads only insomuch as we think them furnishing the means of more rapid and economical transport. If a better method was proposed we should not hesitate to give it

our humble support. It would be going too far to say our opinion of the superiority of railroads is shaken as far as we have yet read in Mr. Gordon's book, and we should be acting uncandid if we did not acknowledge that several of his arguments and positions could not, in our opinion, be easily answered. We have ever thought that steam-carriages can be made to run with comfort and convenience on common roads, but whether they will at any time be made to rival railroads in celerity and cheapness is a question not less difficult than important, and which, for the present tense, must be answered in the negative. However, we purpose to give this subject our best consideration, and if our opinion should then be changed we hope we shall not want candour to own it. In the meantime we can recommend Mr. Gordon's book as containing a better history of what has been done with steam on common roads, and as detailing more facts connected with the practical operation of the subject than we have yet seen in any other author. His history of the invention and progress of improvements in locomotive boilers is particularly deserving of attention; the great drawback is that his plates are not good and are badly lettered.

SCIENTIFIC AND MISCELLANEOUS INFORMATION.

Irradiation of Light.-It is a curious fact that if the same letters of the same size precisely are painted on two boards, the one white on a black ground, and the other black on a white ground, that the white letters will appear larger and be read at a greater distance than the black. This is owing to what is called the irradiation of light. It depends on this that the impression made on the bottom of the eye by bright objects, extends a little wider than the actual portion of the organ struck by the light, and invading the space occupied by the darker objects makes the brighter appear larger than they really are.

Astronomical Phænomenon.-A curious phænomenon in astronomy, is, that a star about to be eclipsed by the moon will actually appear to advance within and upon her bright part, and "sometimes considerably" before it disappears behind her. This has been considered to be a very difficult phænomenon to explain. We have no doubt but it is referable to the same principle that makes the illumined part of the moon appear, when the moon is a day or two old, so much larger than the darker part, and actually to clasp it. This phænomenon, which is partly owing to irradiation, and partly, perhaps, to the lunar light a little beyond the visible part of the moon being bent by the moon's attraction towards a point on one side of her, extends her apparent diameter beyond her real. Hence the more vivid light of the star will

appear through the false diameter of the moon, and will not disappear until interrupted by her real body. If this explanation be true, the phænomenon will be more marked the brighter the star, and the farther the moon's path is from the centre of the star at the time of the occultation, the longer also will it continue. It ought also equally to hold good at the emersion if it happen in the illumined part of the moon.

A Long Yarn." A bale of Demarara cotton can be spun, and is made into thread, which would reach from the earth to the moon."-Gordon's Treatise upon Elemental Locomotion, p. 342.

We may with propriety call spinning this thread 240,000 miles "spinning a long yarn." We only want Perkins's steam gun to carry one end of it, and twist it round the neck of a lunarian, to execute him according to terrestrial law.

"The Turnpike Roads of England and Wales alone, exclusive of highways, extend 19,800 miles in length."-Ibid, p. 343.

If we have to make railroads in lieu of all these, civil engineers, Parliamentary agents, barristers, attorneys, surveyors, &c. &c. &c. will have a glorious time of it for some years to come.

Supposing these lines to occupy six acres to the mile, they would take up 118,800 acres of land, and would cost, at the low estimate of 12,000l. per mile, 237,600,000l., about half of which we presume would be spent in labour. If they were rated to the poor at 2s. in the pound, on barely the interest of their cost, they would produce rates collectively amounting to 7,128,000l. per annum, that is somewhere about one million less than the total sum at present collected for poor-rates, or ths of the whole. This is independent of the employment they will give afterwards, and the trade they will create. Who after this will say railroads, when completed, will not help us in our burthens? Assuming we could spend £10,000,000 per annum on them, they would take 233 years to complete, and at only 200 tons of iron per mile, would consume near four million tons of iron in the rails, besides iron for the engines, carriages, &c. &c.

Calculations of this sort are easily made, but who could tell us how many hundred thousand lies per mile the counsel and witnesses will tell to carry the lines through the committees ? Really, if things go on as they have in committees, his Satanic majesty must enlarge his dominions, and provide extra room for the increased population he may expect of lawyers, engineers, and professional witnesses.

Hydrostatic Carriage." A mechanician of Haunkenzell, in Rhenish Bavaria, named Schmidtbauer, has invented a carriage of very simple machinery, which he puts in motion by the application of the hydrostatic process. This vehicle runs on ordinary roads at the rate of about 16 leagues an hour! The model of it has been purchased by an English house."-Journal du Commerce d'Anvers.

New Locomotive Power.-Mr. Mullins, M.P. for Kerry, has made a very important discovery in the scientific world, that of applying galvanism, instead of steam, for propelling vessels and carriages. He is now building a carriage upon this principle, and several of the first engineers who have seen it, say there is every prospect of success, and that it will supersede steam.-Limerick Star. The Dublin Evening Post claims the merit of this invention for the Rev. J. W. M'Gawley, one of the clergymen of the Roman Catholic cathedral of that city, who, that journal says, explained it at the meeting of the British Association there last August. "The discovery," proceeds our Dublin contemporary, "has excited interest among the savans of Germany by Mr. M'Gawley's interesting and important invention, which is to form one of the most attractive features of the British Association at its approaching meeting in Bristol.- Worcester Journal, 10th August.

British Scientific Association.-The most splendid meeting ever held by the Association has just been closed at Bristol. This city has done itself great honour by the spirited and munificent manner in which it has received the Association, and by the liberality with which every thing valuable and worth seeing has been thrown open to the members. The chief difficulty experienced was owing to the separation of the sectional Committees in distant parts of the city, which, however, was unavoidable. Some valuable communications have been made to the sections in mathematics, physics, chemistry, geology, &c. &e., but very little with respect to railways. Indeed, we have seen with surprise how little men of science appear to understand this subject, now one of the most important to civilized society. In our next we may have an opportunity of adverting to a discussion that took place between Mr. Davies Gilbert, Professor Mosely, Dr. Lardner, and the Editor of this Journal, which will fully bear out the observation we have made.

PROGRESS OF RAILWAY WORKS.

LONDON AND BIRMINGHAM RAILWAY COMPANY.

Sixth Half-Yearly General Meeting of the Court of Proprietors.

EXTRACTS FROM THE REPORT.

Birmingham, August, 1836.

THE Directors have the satisfaction to announce to the proprietors, that the progress of the works generally, in the last six months, has been such as to warrant the expectation which was held out at the last meeting, that the whole line will be completed