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PILBROW'S CONDENSING CYLINDER ENGine.

else remained the same. To the 2nd I would first observe, that in the common engine every alternate stroke has to eject the condensement, therefore there must be some irregularity here; but in mine, half that quantity is ejected at the termination of each stroke, (calling, here, half a revolution a stroke.) As to the injurious effect of ejecting the condensement in so short a period by a large piston, "when the crank is in the worst possible position to carry on the movement of the engine," I must say I consider the contrary. Those well acquainted with the steam-engine, and its precise regulation, know that it is desirable that all the momentum and elastic force of the steam, above the amount necessary to simply overcome the friction of the engine, should be taken from it before the turn of the stroke, so that it should not be expended upon the matter of the machine itself. To accomplish this, it is the practice in many of the best engines to let in the steam upon the eduction side of the piston, before the stroke is quite completed, or in shutting the late eduction valve, and opening the contrary, prior to the turn of the piston, to bring all to a perfect and positive easy rest. Now, such proceedings are accompanied with loss of duty and steam; but when the engine is properly regulated, the momentum acquired by the descent or ascent of the pistons, and all the machinery therewith connected, will be taken up by force necessary for the expulsion of the condensement, &c., to the atmosphere. This action will not be a sudden jerk or concussion, as some have supposed, (as I have before fully explained,) but a gradual oozing, rather, of the condensement; when the momentum of the matter has the greatest power over the cranks, instead of the worst; when the crank may have to move twelve times as fast, and twelve times the distance of the condenser piston, which gives, of course, that proportion of mechanical advantage. If N. N. L. doubts the accumulation of power, or a concentrated force doing as much as a "diffused" force, let him think of the various stamping machines. As to that part relating to the better vacuum and the accumulation in the condenser, although N. N. L. has in great measure answered himself, and saved me the trouble, I shall simply say, that when there is a separate condenser, according to the proportion the same bears to the air-pump, so will the accumulation of gases be; for if the air-pump is of the same capacity as the condenser, then must there be, at the time the air-pump makes its stroke, double the quantity thrown in by the steam cylinder and injection each stroke, or the air-pump could not take out as much

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as was thrown in; and when the air-pump is only a single-acting one, this accumulation is again doubled. All this I have said over and over again, and nothing but this can be inferred from it; not that I suppose less is taken out than is thrown in. I am obliged, however, to N. N. L. for his notice, and shall be happy to meet him again, if he is not satisfied with my hasty reply.-J. P.

PILBROW'S CONDENSING CYLINDER

ENGINE.

Sir, This invention has been so much discussed in your pages, that I should not join in it, but for my promise some time back, particularly as Mr. Pilbrow has, I think, answered satisfactorily the objections made to its principle. Whether, however, there will be that perfect equilibrium necessary to give it so great a superiority over the present engine, is a point that practice alone can determine, though I do not see any theoretical law to prevent it.

In Mr. Pilbrow's reply to my question, respecting the consumption of fuel by the best marine engines, he has shown the difficulty of determining the quantity with any accuracy, owing to the frequent variation of the actual power by cutting off the steam at different parts of the stroke. I regret I cannot help him to a nicer appreciation; but there are few facts taken with sufficient accuracy to determine the real amount; and it is to be lamented that the suggestion of one of your correspondents has not been adopted, and the returns of fuel consumed made in the form of his log. Until this is done, I think no dependence can be placed on bare statements of only 5 lbs. per actual horse power, from whatever quarter they may come; for I have little doubt that this return has been made from the total quantity of coals consumed on a voyage, calculated upon the extreme actual power, worked to the utmost, when the diagrams have been taken, but which extreme has not been continued more than one-fourth the whole distance.

Although I think it will be found, on a proper comparison, that, making allowance for the gain in duty by expansion, the engines of the present day consume, on the average, nearly as much coal as the average of Mr. Watt's engines, there is certainly not so great a difference be

tween the cylinder exhaustion and condenser vacuum of the best modern engines as in those of Mr. Watt; and the apparent improvement in modern practice is so great, that it ought to give a corresponding increase of duty, but it does not. Either the results, therefore, of Mr. Watt's engines, given by Mr. Farey, are inaccurately reported, or no reliance can be placed upon the vague and ever-varying assertions of consumption of the present engines. Whatever may be the cylinder exhaustion of the average of engines, the best, using steam expansively as low, nearly, as it can be used, are within three-quarters of a pound of the condenser vacuum; an approximation as near to perfection, probably, as the action of the steam-engine will permit. But I certainly agree with Mr. Pilbrow, that this excellent evacuation is only obtained by an equal loss of steam power, by opening the exhausting valve before the completion of the stroke; so that there is a total loss equal to 14 lbs. on the square inch, even in the best engines. Assuming, then, that Mr. Pilbrow's engine will maintain an equilibrium throughout the stroke, there can be no doubt, I think, that it will be superior to the most excellent marine engine that can be made, to the extent of 1 lb. the square inch, in this particular, and probably to half a pound more for a better extreme vacuum, giving a total gain of 2 lbs. That such an invention must inevitably supersede the separate condenser engine of Mr. Watt, I see no reason to doubt, and I cannot give the talented inventor higher praise. It certainly has the merit of being the most original, as well as the soundest based improvement on the steam-engine since 1765, amidst the thousand attempts made since then to improve Mr. Watt's. S. has justly observed, that Mr. Pilbrow's engine is contending with a substantial, not a shadowy defect in the present engines; and as it is yet more simple than Mr. Watt's, and cheaper, it seems to me that Mr. Pilbrow may claim the merit of having brought the reciprocating engine to the highest perfection of economy in fuel that its nature is capable of. It seems to me that the condensing cylinder engine is a valuable contribution to mechanical and philosophical science.

To prevent any jar, Mr. Pilbrow will

probably find it better in practice to increase the area of his condensing cylinder, (keeping the capacity, of course, the same as the steam cylinder,) as its speed will be double that of the present air-pumps, which might render the discharge of the condensement somewhat inconvenient. This additional speed may prevent the speed of the piston being increased to 400 feet a minute, as Mr. Pilbrow contemplates, to obtain double the power in the same space.

There are now four inventions before the public, of the very highest importance to steam navigation; sound in principle, and, except the first, amply confirmed by practice. The condensing cylinder engine of Mr. Pilbrow; the condensation by injection, to prevent incrustation, of Mr. Symington; the prevention of smoke of Mr. C. W. Williams; and the screw propeller of Mr. Smith. Britain, it is gratifying to see, still maintains her station, the first in the mechanical and useful arts. She has now put at the disposal of commerce new means of extending it, of removing many acknowledged evils of steam navigation, and yet what an amount of prejudice has talent to overcome! People will not believe their sight! Every thing changes-states, cities, empires, nations, the earth and sea-all progressing to some wondrous close; but the human mind remains "cribbed, cabined, and confined," bound up in prejudice, and we see now in operation what so long retarded the introduction of Mr. Watt's engine, three quarters of a century ago. Is it written that the mind alone shall never progress from a bondage that has in all ages debased it! I am, Sir, your obedient servant, January 29, 1842.

SCALPEL.

MALLET'S HYDRO-PNEUMATIC BUFFERS

-IMPROVEMENT SUGGESTED.

Sir, It is with some degree of diffidence that I come forward to suggest an improvement in the invention of a practical engineer, like Mr. Mallet; who may be supposed to have well considered the precise bearing and effect of his combinations, and to have adopted the best and most appropriate means, for making his invention practically perfect. I make this observation, preparatory to referring

MALLET'S HYDRO-PNEUMATIC BUFFERS.

to a part of Mr. M.'s ingenious hydropneumatic buffers, described in your No. 956, which has struck me as far from exhibiting the adaptation of well devised means to obtain the best results. I allude to the means adopted by Mr. M. for preventing the plunger being driven out of the cylinder by the rebound or recoil of the compressed air, which is done by projecting fillets cast on the inner end of the plunger, which impinge against the cylinder on the recoil of the plunger. But, so far as I am able to understand Mr. M.'s description, his invention contains no provision for preventing or counteracting the sudden shock or concussion with which the inner end of the plunger must thus be driven against the cylinder by the reaction of the compressed air.

A very simple expedient offers itself, by which the plunger may be as effectually prevented from being driven out of the cylinder, as it can by fillets or any other mechanical resistance, while at the same time the possibility of any shock or concussion is entirely obviated. For this purpose it is only necessary to employ a double hollow plunger, divided into two equal parts and working through both ends of the cylinder. The following fig. and accompanying description will render this more plain.

C

B

A is the cylinder, truly bored, and mewhat longer than the double (and

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partly) hollow plunger B, which works through both ends of the cylinder in stuffed collars, and is divided into two equal parts 1, 2, by a metallic plate or diaphragm, which projects so as to be capable of being formed by any appropriate means into a piston, working smoothly in the cylinder. One end of the plunger is armed with the usual buffer-head; C, the other end, is plain and concealed in the frame work of the carriage. The apertures of the two air chambers of the plunger, communicating with the cylinder, are near to each side of the piston and in the lowest part of the plunger.

Now it is obvious, that if the air in each division of the plunger be in an equal state of compression, the latter will necessarily be in the position represented in the drawing with the piston exactly in the middle of the cylinder, and the buffer at rest. On coming into collision with another body, the buffer will be driven in, more or less, according to the force of the collision, and the air in the farther chamber (2) of the plunger compressed accordingly. But whatever may have been the force of the collision, and degree of compression, the plunger cannot, on removal of the impulsive force, fly back or rebound with a sudden shock against the end of the cylinder as in Mr. M.'s arrangement: for as soon as the piston passes the middle of the cylinder on its return, the air in the near compartment (1) of the plunger begins in similar manner to undergo an increasing compression, which will not only destroy the force of the recoil, before the piston comes near the end of the cylinder, but re-act on the opposite end, in its turn; thus establishing an oscillating motion of the two ends of the plunger, until the buffer finally comes to rest, with the piston in its old position in the middle of the cylinder.

As a concluding suggestion, let me ask whether oil would not be a better fluid for using in the cylinder than water? Oil would lubricate and make the different parts of the buffing apparatus work with greater ease and delicacy of movement; and the freezing point of certain oils is considerably lower than that of water. The quantity required for each buffer would be trifling.

January, 1842.

N. N. L.

MR. C. W. WILLIAM'S IMPROVED BOILERS -IMPROVEMENT SUGGESTED.

Sir,-Will you permit me to recommend, through the medium of your journal, the adoption of ribbed plates, as represented in the above sketches, in lieu of Mr. C. W. Williams's cylindrical conductors, one portion of which that gentleman admits there is a difficulty in introducing, on account of their interfering with the removal of deposited matter. These ribbed plates would admit of a great extent of heating surface, and would offer no greater obstacles to a cleansing process than common ones. I am, Sir, your obedient servant, C. W.

PROTECTION OF THATCHED COTTAGES FROM FIRE ARCHIMEDEAN SCREW PROPELLERS-THE BUDE LIGHT, &c. Sir,-In my letter of last week, on the prevention of fires, I forgot to mention an effective means of rendering the thatch of cottages, barns, &c., incombustible. It consists in soaking the thatch with whitewash made of lime, or whitening and size, in the usual way, to every four gallons of which is added one pound, or rather more, of alum. Alum would suffice by itself, but the rain would wash it off.

The lime and size form a film over every straw, insoluble in water. In July, 1835, I covered a quantity of straw and perfectly dry furze with this cheap preservation, and, after it was well dried in the sun, I endeavoured in vain to make it burn. I do not pretend that this wash can, with expediency, be applied to the vertical sides of a hay-stack, because, first, it would not penetrate sufficiently; secondly, the quadrupeds would not like it. Whether the wash would be best applied to the straw before being bound into a thatch, or afterwards, a trial or two would determine. If deal boards are well soaked in a strong solution

of alum, I should not like to have the task of setting them on fire with the best roche à feu, (in English, wild-fire, or carcass composition,) even my own, which Woolwich authorities have told me is stronger than Congreve's; it burns a hole through an iron plate, and consumes an iron bolt, a quarter of an inch diameter, in a few minutes.

Whilst I have my pen in my hand, I will take the liberty to touch upon another trifling thing or two, until I have time and means to give you something better, which will be soon.

"I hope I don't intrude," if I venture to say a word or two about the Archimedean screw propeller for steam-vessels. In your Number 961 there is a long account of "A Trip in the Archimedes" steam-ship. Now, although I have already mentioned the fact, I do not think it impertinent for me to take the liberty of repeating it, i. e. that it was I who presented the plan, with models and drawings of this said screw propeller, to the Duke of Clarence, Lord High Admiral, in 1837. Admiral Sir Edward Owen was then his secretary, or chief counsellor; I have his letters to show that my plan was rejected as inefficient! Many other things, which on occasion of the first war will surprise the belligerents, were also disregarded. So much for that.

Another item is, that I see a patent taken out for a light caused by the proJection of a jet of hydro-oxygen gas on to a cylinder of lime. It was Mr. Goldsworthy Gurney who invented that mode of producing an intense light, at his residence of Bude, in Cornwall, in the year 1825 at least, that was the year in which I first saw it. This light afterwards got the name of the "Drummond Light"-how, I do not know: but Lieutenant Drummond was a gentleman well connected, and belonging to the British service!

The season and the weather prompt me to write a word on humidity. În 1816, I lived for some time near Tonbridge-wells, in Kent. In very dry summer weather, I observed patches of grass quite green, while others were browndried up by the sun. I thought it right to examine the cause, and, by a few strokes of a spade, I found that there was a stratum of chalk in contact with the roots of the grass. This guided m

SKATING FOR LADIES.

Some

to several reflections. I thought that chalk had a greater disposition to attract and retain the moisture of the atmosphere than other earths, and I have still reason to be of that opinion. I also observed that the large earth-worms, (lombrici,) never came up to defile the turf when it was upon a layer of chalk. So the first application of my remarks was to persuade my friends Mr. Campfield, Mr. Saint, Mr. Woodgate, the banker, and some others, who had their wives' and daughters' shoes daily soiled by the worms' projections on their lawns, to allow me to take up the turf, and replace it, after putting under it a thin stratum of chalk, broken about as fine as the coal used in smiths' forges: but the finer the better. I did all this in June, 1816, and not a worm ever came up afterwards; besides that the turf always retained its verdure, in the driest weather. years after, I observed on my garden walks, during a frost, especially when conjoined with fog, a circumstance which went some way to confirm me in my guess at the humidity-attractive disposition of chalk. I observed that a piece of chalk, exposed to the frost, accumulated around it more than five times its own weight of ice, and after a few frosty foggy nights, the bit of chalk became as a speck in the centre of the surrounding ice. After frequently remarking this fact, I bethought me of trying whether other substances would become equally covered with ice, under similar circumstances. I placed in propinquity, on the same path in my garden, bits of wood, orange-peel, cork, marble, iron, lead, and glass, all of the same sizes and shapes. I have not now access to my memoranda on this subject; but, as far as I can remember, the iron and lead accumulated no ice; the cork scarcely any; the orange-peel a little; the marble rather more; the wood, (deal,) a little; but the chalk, after a few days' and nights' exposure, was surrounded by at least six times its own weight of ice. I leave this experiment in the hands of philosophers to try at a cheap rate.

Now we must teach the ladies to skait, without the possibility of a fall whilst learning. In 1816, I had constructed some bell-shaped things of wicker-work, just fitting round the chest, under the arms, but expanding at the bottom to about four feet diameter-it might be more. Shoulder-straps prevent its touch

107

ing the ice; but upon a trip which, sans the basket go-cart, would have been a fall, the machine, (if we may so call it,) rests and slides upon the ice, supporting the lady under the arms on a well-padded rim. This is no joke, for I put it to a successful test at Groombridge, in Kent, in 1816. However, I do not suppose that the ladies will avail themselves of the suggestion.

I hope that my next letter will contain something better than the trivialities of this. By the by, Sir, do you know-I dare say you do the origin of the word "trivial?" The ancient Roman roads were formed of a carriage-way, and a foot-path on each side, as are most of ours; hence they were called tri viæ, or three ways. But the word "trivial" used to mean, with the ancient Romans, any thing well known, and common, and spoken of on the high roads, or tri viæ. The triumphal arch at Hyde-park-corner sins sadly in having only one centre passage for carriages, which formation makes it look very heavy. All Roman triumphal arches have three openings-tri viæ. I have the honour to be, Sir,

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Sir,-Being anxious to try some experiments on voltaic electricity, and to construct a large coil machine, but, for want of pecuniary means, unable to procure the requisite quantity of "insulated copper wire,' it occurred to me that fine tow might be so thrown on as to answer the intended purpose. I immediately applied to Mr. Dinmore, rope manufacturer, at Woolwich, and suggested the possibility of effecting my object by stretching the wire from the wheel, and giv. ing it a rotary motion, while it was fed sideways by a person walking: the experiment was tried, and found to answer admirably. Thus, by this means, an immense length of wire can be covered at a most insignificant cost. To render it more compact and secure, I give it a coat of some resinous varnish after each coil on the reel. When a secondary wire is required, you have only to throw them together by the ordinary method of spinning twine.

By reference to the undersigned, any quantity of this wire can be procured. J. WALKER.

Woolwich, January 11, 1842.

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