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Atmosphere.

CORNWALL POLYTECHNIC SOCIETY.

The preceding extract is introductory to a set of tables, by Mr. Enys, "relative to the properties and practical application of steam, which are of such general interest, and calculated to be of such extensive utility, that we need make no apology for transferring them, along with some further preliminary remarks, to our pages.

"The simplest form of calculating the moving power of steam, is the extension to all pressures of the mode employed by Tredgold for the power of steam of atmospheric pressure. The term efficiency used in these tables, was suggested in a paper published in the Transactions of the Royal Society, in 1827, by Mr. Davies Gilbert: this word prevents confusion with engineer's power, or horse power, which is available efficiency, or the neat power of the engine applicable to the owner's use. It is equivalent to "The power of steam to produce motion" of Tredgold; "The power exerted by steam" of Wood on Railways; "Mechanical power of steam." A similar distinction is also required between the gross work, including inertia, friction, &c., and the neat work done. Effect may be applied to the former; Duty to the latter.

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CORNWALL POLYTECHNIC SOCIETY.

Illustrative of the advantage of working High Steam expansively, as practised in Cornwall. TABLE 3.

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66

We are glad to observe, that among the premiums offered through the medium of the Society for the current year, (and very liberally not confined to the county,)" there are two by Mr. H. H. Price, C. E., "for the best, and second best practical plans for adapting to steamvessels" that method of working steam expansively, the advantage of which, is so strikingly demonstrated by the preceding tables. It is accompanied, however, by this very proper caution, that "due regard must be had to the essential difference between a single-acting engine working pumps by a lever, and two double-acting engines working with a crank."

The premium offered last year by the Society, for the best method of measuring the length of the stroke of the piston, has been awarded to a counter invented by Mr. M. Loam, which is about to be introduced in the United Consols mines. This apparatus is admitted, however, to have two serious defects; in the first place, it registers only the number of

strokes made by the piston, and not necessarily the space through which it passes; and secondly, it derives its motion from the bob through a lever, so that it measures the arc of a circle instead of the tangent to it; in other words, it shows the distance passed over by the end of the working beam instead of that travelled by the piston. Something much better is therefore still wanted.

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Another of the steam-engine desiderata of last year was an exact method of measuring, and registering the exact quantity of water supplied to the boiler." This is now considered to be fully supplied by the water-meter of Captain T. Richards, of Wheel Vor, of which a drawing and description are given in the present Report. The principle on which this meter is constructed is that a vertical measuring pole, and the parts connected with it, shall be thrown out of action whenever the feed is turned off, but driven down and forced up by the water whenever it is passing into the boiler, and that this shall not take place without acting on a counter, and registering the quantity delivered by showing the number of inches the pole has gone over in its down stroke. Mr. Richards proposes that the measuring pole should be of such diameter that the cubic content of every inch in length should be equal to a quart of water, in which case the indications of the counter would be in quarts. In this plan there are no additional valves

LONDON GRAND JUNCTION RAILWAY.

or cocks, and the only part requiring adjustment is a stuffing-box for the measuring pole.

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A premium which was offered last year by J. Buller, Esq., for the best essay on the natural history of the pilchard, has produced an exceedingly interesting paper on the subject by Mr. Jonathan Couch, from which, however, we can only afford room for one brief extract:

"The quantity of pilchards caught on the coast of Cornwall, can scarcely be made the subject of ealculation, since no account is taken of what is reserved for home consumption; we therefore can only here remark on what has been recorded to have been exported. The largest schuls are found late in the season, and commonly in sheltered situations, at a time when the weather is troubled. A few years since, a capture was made in Hemmick Bay, to the amount of two thousand two hundred hogsheads; and Borlase reports the taking of three thousand hogsheads at one shooting of the sean: but even this is not the greatest on record; for, in November, 1834, it is said that three thousand five hundred hogsheads were landed from one sean at St. Ives; and on another occasion, ten thousand hogsheads were enclosed in that port in one day, though not in one sean; thus producing the enormous multitude of thirty millions of living creatures drawn at once from the ocean, for human sustenance.

"The greatest number I was ever witness to, as taken in a drift-boat, was 40,000, but I have been informed, on credible testimony, of 80,000 taken at once, in a single capture; and it was supposed that this alleged number fell short of the whole. About the middle of the eighteenth century, it was not uncommon for the drift-boats to get so much fish entangled in their nets, that they were obliged to sacrifice a portion, by giving some of their nets and all their contents, to those who would take care of them, on condition that the nets were returned to them again within a few days: the condition was, assistance in securing the remainder."

Besides the articles we have thus particularly noticed, there is an Essay "on the various Diseases incidental to Miners, their Causes, &c.," by C. Carlyon, M.D., which as a first but able contribution to an important brauch of medical statistics too much neglected, deserves, and we hope will attract, the attention of the author's professional brethren; a description of some improvements made since last year by Mr. R. W. Fox on his dipping needle deflector, (see Mechanics' Magazine, vol. xxiii, p. 97,) and a chart and table showing" the dip and intensity of

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the terrestrial magnetism in different parts of England, Ireland, and Wales," as ascertained by this deflector; and no tices of several inventions favourably thought of by the Society, though not comprehended within the scope of its premiums, such as Hoskin's Portable Punching Press (the engraving and description of which we gave in our last number), Wilton's Miners' Theodolite, Loam's Wheel Wrench, &c.

We are pleased to find it reported that the funds of the Society are, as they deserve to be," in a flourishing condition." "Their means have exceeded their dis bursements." Happy would it be for nations, as well as individuals, were they to keep always within the same prudent limits. Of the evil consequences of exceeding them, a memorable illustration is furnished by an item in this annual budget of our Cornish friends, which still remains to be noticed. The item to which we allude is a "Chronologi cal Map of the Wars of the British Empire from the revolution in 1688-9 to 1835," showing how, from small begin nings from a mathematical line without depth or breadth our national debt increased (though the wars aforesaid, and all the destruction of life and property of which wars are the invariable cause) to a seam of 860 millions thick!!!

LONDON GRAND JUNCTION RAILWAY. (From Report of the House of Commons Committee, on the Bill for this Railway.)

By an Act passed in the third year of his present Majesty's reign, a Company was empowered to make a railway from Birmingham to London, terminating on the north side of the Regent's Canal, Camden Town. In the last session, an Act was passed for making a branch from that point to Euston-grove, in the parish of St. Pancras, for the conveyance of passengers and light parcels only, but not of merchandise and goods. There are at present, therefore, no means for the conveyance of the present number of passengers proceeding from Camden Town to the City, or for those who. will be brought by the Birmingham Railway, except the ordinary vehicles plying in the streets. The only present means for the conveyance of goods from Camden Town is the canal, but as that is at no point nearer the City than the

8.

THE PNEUMATIC RAILWAY.

New-road, it could not be available for that purpose. Evidence was adduced to show that it would be a great advantage to trade and commerce to have a railway communication for goods and passengers extended to the City.

The amount of income expected to arise from the conveyance of passengers and goods is 113,5597., of which 90,8187. is expected from the conveyance of passengers, and 22,7417. from the conveyance of goods which are the manufactured articles of Birmingham, Manchester, and other manufacturing towns, and live and dead cattle to Smithfield, Newgate, and Farringdon markets.

The proposed railway is the extension and completion of the Birmingham Railway, and is an integral line between its respective termini.

The only line which can be considered as a competing one is an inclined plane, now in progress, from the Birminghamn Railway at Camden Town to Eustongrove, a distance of nearly a mile; but that is only enabled to convey passengers and light parcels. The proposed railway has the advantage of conveying passengers to the centre of the metropolis, about three times that distance, yet at one-fourth less charge. It is also to be adapted for the conveyance of goods, which would otherwise have to be carted from Camden Town.

The whole line will be worked by locomotive engines, without any assistant or stationary power.

There seems to be no peculiar engineering difficulties in the proposed line.

There are no tunnels.

The steepest gradient is 1 in 273, or 19 feet in a inile. The smallest radius of a curve is half a mile."

The length of the line of railroad is two miles and fifty chains. There are no branches.

The plan seems, in an engineering point of view, well fitted for the objects intended.

No turnpike road will be crossed by the proposed railway on a level.

The estimated cost of the whole work, including the cost of property, is 600,0007. This estimate was proved by George Rennie, Esq, and supported by the evidence of Colonel Landmann, the engineer of the Greenwich Railway, as respects the engineering department; and by George Smith, Esq., and Wil

liam Barnes, Esq., surveyors, in the city of London, as to the valuation of the property to be purchased. Your Committee, therefore, see no reason to apprehend it will be insufficient.

The estimated annual charge for the railroad, when completed, including all incidental expenses, is 40,0007., which was founded on the charges of similar works now completed.

The evidence fully satisfied your Committee that the return would be sufficient to support all the annual charges and maintenance of the railroad, and leave an adequate profit for the shareholders.

Your Committee think it desirable the House should be informed that, as this railroad follows the course of the River Fleet, a considerable portion of the ground is not built upon; so that, in fact, the arches under the railway will form as many dwellings as the railway will displace.

A great part of the houses that will be taken down in and about Hattongarden and Saffron-hill are in a dilapidated and dangerous condition. Several parochial officers gave evidence as to the state of the neighbourhood, and the advantage it would be to have an opening made through that confined and unhealthy part of London.

THE PNEUMATIC RAILWAY.

Sir,-The peculiar formation of the air tubes which, in one way or other, are intended to form the carriage way of the projected pneumatic railway, appears to be that to which the attention of the public has been especially directed in the various articles which have appeared in the Mechanics' Magazine on this subject; but I am not aware that any thing bearing expressly on the mode of procuring the current of air in the tubes has been published. It seems intended that steam, applied through the instrumentality of stationary engines, should be the generator of power, and that this power should be employed to extract the air of the tubes through the agency of air-pumps. Have not some objections been made to this agency, raised upon the reciprocating action of the pumps, and the elastic nature of the element to be operated upon? If these objections have been thought formidable, might they not both be overcome by the simple application of fans instead of pumps, which are now

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