A FEW MORE OBJECTIONS TO THE

PNEUMATIC RAILWAY.

Sir,-The inventor and approvers of the Pneumatic Railway seem to have overlooked the following objections :—

1st. On the proposed construction, however great the load required to be conveyed on the line in a given time, not more than a certain fixed and constant quantity can by any means be conveyed.

2. However small the load to be conveyed, the expenditure of power would be the same, as if the maximum load were conveyed.

3d. So far from the Pneumatic Railway doing away with the necessity of levelling the line, the necessity becomes increased fifty-fold. From Dr. Lardner's statements it appears that 1 ton moved perpendicularly will equal 200 tons inoved horizontally. Now, if on any part of the line, between two fixed engines, there were an inclined plane, rising, say I foot in 10, the capability of the Pneumatic Railway would be diminished to the following extent :-Let a be the power required to move 1 ton horizontally, then a x 200 the power to move 1 ton perpendicularly; and ax 200

+a, the power required to move 10 1 ton up the supposed inclined plane. Therefore, as the power is constant, if the inclined plane were only 1 foot long, yet only of the load which could be conveyed on a perfect level could be conveyed on the one supposed.

4th. Dr. Lardner states, that if such a degree of rarefaction were produced in the tunnel as would cause the mercury to fall 2 inches, an impulsion equal to 200 tons on a piston of 40 inches diameter would be produced. This is true, but the impulsion would only continue for 4th of the length of the tunnel, when the load would stop. The fact is, the tunnel must be entirely cleared of air to cause the load to move through the whole length; but, according to the data laid down by the Doctor, and which I see no reason to dispute, the area of the section need only beth of the size proposed, to move 100 tons along.

Were the tunnel to have a square section, and be enlarged, in those parts of the line in which there is a rise, in proportion to the power required, and the

THE SAFETY-LAMP NOT SAFE.

Sir, It is a lamentable fact that, year after year, hundreds of those industrious, and it is fair to assume, careful men the working colliers-are destroyed by the ignition of the inflammable air of coal-mines, while under the alleged protection of the Davy lamp; and that, too, in the best regulated collieries. This fact calls at once, in the name of justice and humanity, for a strict and immediate inquiry. Has the miner, or not, a protection in the lamp to the extent represented by Sir H. Davy? And if its pretensions are founded on false data (which there is but too strong reason to apprehend), is it not high time that the miner should be warned against leaning any longer on a broken staff?

The first point to examine is, what are the pretensions of the lamp? It will not be invidious to refer for information to Sir H. Davy himself, nor to some other eminent men, who, since his death, have expressed themselves very strongly on the subject. Sir H. Davy states, in his pamphlet on Flame, p. 41 (a work evidently intended for the working miner's government in the use of the lamp), that "he has discovered a lamp which will burn in any explosive mixture of fire-damp, the light of which arises from the combustion of the fire damp itself." The instrument to which he here refers is the present Davy lamp. He also states that the miner may work in fire-damp, if protected, as he asserts he is, from its ignition by this lamp. Mr. Buddle, whose authority is indisputable on this point, estimates the value of the Davy lamp, on the supposition that it would enable the miner to work with safety in an

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an

explosive atmosphere. He observes, in a letter addressed to Sir H. Davy, and published by him in the last edition of the work referred to, 1825, "that when the circulating current becomes explosive, only give the collier his Davy lamp, and he goes to his occupation with the same confidence in this impure atmosphere, that he would in any other situation with a candle." Dr. Üre, ia his otherwise valuable Dictionary of Chemistry, p. 358, calls this lamp infallible protector;" and states, that no explosive accidents have ever happened in coal-mines since its introduction, but from the criminal daring and carelessness of the miner." Dr. Faraday, even since the late explosiou at the Springwell Colliery, when four persons. were deprived of life, and many dreadfully injured, spoke of it as a monument of the powerful genius of Sir H. Davy;" and Professor Brande affirmed, in a recent lecture at the Royal Institution, that he still believed the Davy lamp to be perfectly safe in all its proper uses;" which " proper uses must, of course, be those so plainly pointed out by Sir H. Davy himself.

"

It will be observed, that neither Sir H. Davy, nor any one of these his intimate and scientific friends, limit the uses of this lamp. They, therefore, sanction the general and fatal error (for such, unhappily, it has proved), that it will enable the miner to remain any indefinite time in an explosive atmo. sphere. It is true that Dr. Turner informed his readers, in a work he has lately published, but which from its price, and its scientific character, cannot be expected to find its way to the miner's hand," that if a lamp, with its gauze red-hot (which it soon becomes in an inflammable atmosphere), he exposed to a current of explosive mixture, the flame may possibly pass so rapidly as not to be cooled below the point of ignition, and in that case an accident might occur with a lamp which would be quite safe in a calm atmosphere." Again, he says, "when the lamp is carried into an atmosphere (a calm one) charged with fire-damp, the flame be gins to enlarge, and the mixture, if highly explosive, takes fire, as soon as it has passed the gauze, and burns on its inner surface." He properly recommends, that "whenever this appear.

ance is observed, the miner should instantly withdraw; for, though the flame be not able to communicate with the explosive mixture on the outside of the lamp (so long as the texture of the wire-gauze remains entire), yet the heat emitted during the combustion is so great, that the wire-guard, if exposed to it for a few minutes, would suffer oxida tion, and fall to pieces;" in which case the terrible event of an explosion must inevitably ensue. Sound and important as this advice is, it happens to be directly opposed to what Sir H. Davy himself has said on the subject, in the pamphlet in question-a striking proof of the great peril to which miners have been exposed, from an implicit reliance on his authority-for, he asserts (p. 135) that "whenever a single wire-gauze lamp is made to burn in a very explosive atmosphere at rest, the heat soon arrives at its maximum, and then diminishes; and the idea of the wiregauze burning out is shown to be unfounded!"

That Sir H. Davy was greatly mistaken in the safety of his lamp, has been unhappily rendered but too manifest, from the dreadful havoc of life so frequently caused by explosions in those coal-mines, where no other light is ad mitted. The result of the trials to which the Davy lamp has been lately subjected by Dr. Turner, and which result has been confirmed by the experiments of several eminent, scientific, and practical men, prove that, in an agitated atmosphere of fire-damp, no reliance whatever ought to be placed on its protection; and that even in a calm, the reliance placed on it should be limited to a few moments. As Sir H. Davy's name, in this case, still carries a dangerous authority, and his errors, therefore, require no common efforts on the part of the press to correct them, I submit this letter to your judgment, in the hope that, as it may by possibility be the means of saving human life, you will consider it worthy of insertion in your much read and influential publication.

I am, Sir,

Your constant reader,
U. G. R.

London, May 5, 1835.

that the engine-crank A is also as represented, then the spring-crank a is on the centre, and the engine-crank A in action (though with a diminishing force). As soon as a is past the centre, it will, by the downward pull of the spring, assist the crank A past its centre, and continue to do so till a is in the position shown by the dotted lines, when it becomes passive. The motion being continued by the engine-crank, which is now gaining power, it begins to bend the spring downwards (consequently storing up power), till the cranks are in the position fig. 4. The spring-crank is now just on the point of refunding the power lent it to assist the steam crank over the lower centre. Thus the steamcrank and the spring-crank do mutually help each other, and a pretty regular motion is produced even without a flywheel.

The principle is here, but the adaptation of it (which admits of innumerable positions of the spring-crank), I leave to the judgment of persons of greater practical acquaintance with the steamengine.

I beg to subscribe myself, Sir,
Yours respectfully,

MICHAEL NOTON, Jun.

Manchester, Feb. 19, 1835.

THE SINGULAR HYDRAULIC

PHENOMENON" (p. 6).

Sir,-In No. 608 of your truly valuable Journal, Mr. Baddeley has described the effects produced by using a short cylindrical branch pipe with a fireengine, which were of "so extraordinary a nature as to surprise all the persons who witnessed the phenomenon."

I am convinced that Mr. Baddeley will not be offended, when I assert that nothing which he has there mentioned as taking place ought to be considered as at all "extraordinary" or "singular." It is very possible that I am wrong in this opinion; and if that should be the case, some of your numerous correspondents will, undoubtedly, be kind enough to correct my mistake.

I would ask Mr. Baddeley-what would be the effect produced on a stream of water flowing through a simple orifice, without any connexion with a pipe? It is an established fact, that the jet of

water issuing through simple orifices is contracted, in a certain degree, in proportion to the extent of that orifice; and what Mr. B. has described as taking place is precisely similar. The opening in the centre of the brass cap may be considered as an orifice not having any connexion with the pipe: the diameter of the pipe is 7-8ths of an inch, and the stream of water was reduced to nearly 5-8ths of an inch, which is very nearly the extent of contraction which takes place in a stream of water issuing from a simple orifice. The area of the contracted vein, to the area of the orifice, differs, according to different experimentalists; but the ratio of 1.62 is generally taken as the more correct quantity. Now, if Mr. Baddeley will calculate the area of the 78th opening, and the area of the jet issuing therefrom-which is said to be something more than 5-8ths— he will find that the result will nearly correspond with the proportion, 1.62. The irregular surface of the jet was, undoubtedly, similar to the irregularity that exists in the stream issuing from apertures acted on merely by gravity. The reason why the jet appeared to issue 7-8ths of an inch in diameter when the engine began work, evidently rose from there not being sufficient force to make the contraction visible; but when the men got into full work, the pressure was increased to carry the contracted vein to a distance from the opening that made it visible. (Query. Was the pipe in an exact vertical position?)

For me to describe to Mr. Baddeley, and the rest of your readers, the currents which exist to produce the vena contracta, would be a great piece of presumption; sufficient is it to say, that the contracted vein must always exist as it issues from openings having no connexion with a pipe; and it cannot be of much consequence whether the fluid be acted on by gravity from above, or by artificial pres sure from below.

I am, dear Sir,
Very truly yours,

Bulbourne, April 25, 1835.

J. L.

MORE PADDLE-WHEEL REMINISCENCES.

Sir, I have perused with pleasure "Scrutator's Reminiscences" of the paddle-wheel, an article which, I hope,

will be the means of saving your readers the trouble of following out the schemes of the so-called inventors, hosts of whom appear, from time to time, in the Mechanics' Magazine, under the titles of projectors, flappers, propellers, windowblinders, parachuters, duck swimmers, screwers, scullers, &c., as it places within one view a good many of the absurd attempts to improve upon the common paddle-wheel. I have also been amused with examining Mr. M'Curdy's propellers, which, though I believe new to that gentleman, were tried by me about six years ago (as already mentioned in the Mechanics' Magazine, No. 582), and were a complete failure, as I afterwards fitted wheels to the boat, which produced much greater speed. The principle was the very same as Mr. M'Curdy's, but f had only two propellers, instead of his four. The objections to them appear to me to be as follows:-1st, The great speed to which they must be driven to make as many strokes as do the blades of the common wheel, and consequent greater amount of friction and weight. 2dly, The propellers, when making their return stroke, in a short head sea or ripple, must just produce as much effect to drive the vessel astern as the immersed ones drive her a-head. 3dly, The great additional breadth necessary, as Mr. M'Curdy's wheel is twelve feet broad, if his cranks have a three feet throw. (It is to be regretted there is no scale attached to the engraving.) 4thly, It would require a very heavy shaft, with so many cranks on it, as shown in Mr. M.'s sketch, and even with great additional strength and weight, it would be a most unsafe thing at sea in bad weather.

Let us examine what speed, for instance, it would be necessary for Mr. M'Curdy's anti-propeller, in such a boat as the Perth, which steams between Dundee and London. That vessel's wheel is about 50 feet in circumference, and makes 20 turns per minute to produce 12 miles an hour; now, suppose the wheel to have 12 float-boards, 6 feet broad (a circumstance I am not sure of, but I have stated it within the mark); thus we have 240 strokes or immersions of the blades per minute. To produce the same effect with the "propellers," the breadth would have to be 24 feet (instead of six); and as each revolution only produces four immersions, it would necessarily require

60 revolutions per minute (instead of 20), a rate of motion, with such a weighty machine, which is impracticable-to say nothing of the additional breadth of 18 feet in each wheel, and the retrograding effects of the back strokes already mentioned.

The superiority of the common wheel seems to consist in its extreme simplicity, and the facility with which it can be driven at a great speed. In whatever way, too, a wave strikes it, or however much the vessel pitches or rolls, every time it touches the water it urges the vessel forward. It is evident, in theory, that the wheel has some disadvantages; but theory and practice do not always agree, and in this case it is undeniable; for, of the immense number of inventions, not one has ever come up to the wheel. And it would now seem that improvements on the wheel itself are likely to be attended with favourable results. I trust these remarks will be thought worthy of a corner in your pages; they are not meant as a critique upon Mr. M'Curdy's invention, but simply to impress upon the minds of inventors the necessity of making a few simple calculations, and looking over the Mechanics' Magazine, to see that nothing of the same kind has been already invented.

I am, Sir,

Your most obedient servant, D. LANDALE.

Wemyss Cottage, April 15, 1835.

THE

HYDRO-PNEUMATIC PUMP," A FALLACY (p. 41). Sir,-The hydro-pneumatic pump of your correspondent W H O, described at p. 41 of your present volume, would indure the belief, that the inventor's acquaintance with "the laws of fluids," to which he refers, is but very slight. His simple apparatus might be extensively useful, but for one or two un fortunate circumstances which prevent its action.

In consequence of a law of nature, which has not been, and is not likely to be repealed, the opening of the exitpipe M (p. 41), must be at least THIRTY FEET below the cylinder A, or the water will not flow out of it! I fancy this would put a new feature upon WHO's invention, and render the machine ex