the case, the plates have to be lapped over each other, and revits put through them both; we may allow, therefore, half the above strength, which leaves 291 lbs resisting strength to the square inch.

It is quite ridiculous to think of such a boiler exploding by fair means; if ever such a thing should occur it will be for want of water, and the fire will burn the iron through with the same facility, whether there be two pounds per inch pressure on the inside, or two hundred. To calculate the strain that a boiler of a square form would sustain, is impossible, without having the boiler in question to look at, as there is generally a number of cross bars in the inside; that go from side to side, to prevent the sides from bulging out with the pressure; with the exception of these stays the comparison of strength between a cylindrical vessel and a square one, turns on this-that the strain to break the iron in the cylinder is in a direction to pull it asunder in its length, and the strain in a square vessel is in a direction to bend or break it across; so it must be

evident to any person who pays the least attention to the matter, that a great deal depends upon how the above stays are fixed, whether well or ill; it likewise requires a great attention, if they are well fixed at first, to keep them so, which is no very easy matter, by reason of the very great and unequal strain they have to undergo, which causes their fastenings at the ends to give way. I have seen a square boiler made with stays as above, and every time the boiler was opened, and that was very frequently, the stays were all adrift, either by breaking, or pulling their fastenings away, or some other cause; at length the boiler, by bulging out by the steam, and collapsing when cold, broke asunder at one time, at an angle to the length of three feet, and by the time that the boilers had been in use for twenty months (undergoing very frequent and expensive repairs in that time) they had to be replaced by entirely new ones, whereas if they had been good cylindric boilers, they ought, and would, have been in use three times as long at least, without any material repairs.

Secondly, to apply the steam when generated, so as to effect the greatest possible duty, or quantity of work, There is only two methods, in which steam can be applied, (properly speaking, whether it be what is called high, or low steam) that is,

letting it flow into the cylinder during the whole length of the stroke of the piston, through the steam admission, or throttle valve, which is opened to a width to admit the steam into the cylinder, at a proper elasticity to perform the duty required, which is the common method; or by opening the steam valve to the full width at the moment that the crank passes the dead points, and allowing it to remain open for a greater or less portion of the stroke of the piston, as the duty the engine may have to do, or the elasticity of the steam in the boiler may require; after which the further supply of steam from the boiler to the cylinder is shut off, allowing the steam that has already entered the cylinder, to expand, to effect the remaining part of the stroke. The latter method is allowed by engineers and others, in general, to be by far the most economical and beneficial; Mr. Watt, at an early period of his improvements, applied it with advantage in his singlestroke pumping engines; the principal reason that it has not been more generally made use of hitherto, has been the want of a simple and effective method of giving the proper supply. Watt's method as applied to his single-stroke pumping engines, is quite inadequate to a doublestroke rotatory engine. But this want for the future need not apply, as the principle may be acted on to the full extent by adopting Mr. Chapman's second improvement in steam-engines, that is, his newly invented expansion gear, which is both scientific and ingenious, simple and efficient, and is under most perfect command by the governor of the engine, where a governor is used, or may be clamped by the engineer in a moment, where there is no governor. It will always open the steam valve at the proper time, and likewise shut the steam from the cylinder at any fractional part of the length of the stroke, so as to keep the engine at any desired rate of motion, let the duty the engine may have to do, or the elasticity of the steam in the boiler, be what

it may. The apparatus is applicable to any kind of steam engine, old or new, land or marine, fixed or locomotive.

Such an apparatus has been long wanted, and I have no doubt but it will become in great demand, as I am informed that the patentee intends to offer it to the public on the most liberal terms.

In support of my assertion of the advantages to be derived from working an engine expansively, it may not be amiss to quote some authorities in favour of it, that can be referred to, and whose evidence cannot be disputed.

The writer of the article "Steam Engine," in the 19th volume of the fourth edition of the Encyclopædia Britanica, page 671, after giving an algebraic solution in proof of his assertion in favour of working by expansion, says :-" Here Mr. Watt observed a remarkable result; the steam expended in this case would have been four times greater than when it was stopped at one fourth, and yet the accumulated pressure is not twice as great, being nearly five-thirds. Onefourth of the steam performs nearly three-fifths of the work, and an equal quantity performs more than twice as much work when thus admitted during one-fourth of the motion." Then he says further "let the steam be stopped at onehalf of the stroke, its performance will be multiplied by one and seven-tenths; if stopped at one-third, its performance will be multiplied by two and one-tenth; if at one-fourth, by two and four-tenths; at one-fifth, by two and six-tenths; at onesixth, two and eight-tenths; and oneseventh, three times as much work, &c.; in comparison to the steam employed, as it would do if the steam flowed into the cylinder during the whole stroke." Mr. Luke Herbert in his Engineers' and Mechanics' Encyclopædia, article "Expansion," after alluding to some other things relating to the expansion of the gases, says, "this property of elastic fluids has been turned to great advantage in steamengines, by admitting steam of high-pressure into the cylinder during a portion of the stroke, and shutting off the communication with the boiler, the expansion of the steam in the cylinder, carries the piston with a constant decreasing force through the remaining portion of the stroke, by which mode of working, the whole effect produced during the expansion of the steam, is clear gain; for example, if the steam be stopped at onefourth of the stroke, the gain would be 150 per cent of the steam employed. If further proof be required, I would refer your readers to the most astonishing duty performed by the Cornish mining engines, as is published in their reports, and other works, all which is effected by expansion.

Mr. Chapman's apparatus consists of a wheel fixed on the principal, or any other axle or shaft of the engine, having a rotatory motion, the circumference of which wheel is a spiral, or curve, generated by the ever-varying motion of the piston in the cylinder, in combination with the angle that the connecting rod forms in its different positions during the revolutions of the crank pin, which spiral acts on a lever which has an advancing and receding motion, effected by the governor, so as to be either a greater or less portion of the stroke in contact with each other, which at every stroke opens the valve at the proper moment, and retains it open for any length of the stroke which the duty of the engine requires, and then closes it suddenly, allowing the steam already entered to effect the remaining part of the stroke.

I apprehend there are few persons who have had an opportunity of observing the working of railway-locomotives, who will not readily coincide with Dr. Lardner's opinion, that the velocity of the pistons is much too great; a slower motion would not only obviate many serious evils attending the rapid reciprocating motion of the apparatus, but it would materially reduce the vibration experienced by passengers in the trains to many persons a source of great annoyance. Whatever reduction may be effected in the relative speed of parts of the machinery, however, it is quite certain that the velocity of transit must at least be sustained. So far as the size of the driving-wheels affects this problem, I incline to the opinion of those engineers who would limit the size of these wheels to six, or at the utmost, to seven feet diameter. To ten feet wheels I am decidedly opposed, and I fancy those persons who advocate the

employment of wheels of such insecure and unwieldy dimensions, will find their advantages altogether fallacious when tried by the unerring test of practice.

"One of the methods," says Dr. Lardner, "by which it has been proposed to render a moderate velocity of the pistons compatible with the extremne speed of progressive motion, which, having once been enjoyed by the public, has become an indispensable necessity in railway transit, is to convey the power of the piston to the working wheels by

tooth and pinion gear. If the practicability of applying this species of mechanism, under the peculiar circumstances of the case of a locomotive engine, be once admitted, we can hardly discover any practical limit to the speed of transit which may be obtained on railways."

"Such a mechanical arrangement," continues this writer, "is so obvious, and founded upon mechanical principles and expedients so well understood, that it cannot be supposed to have escaped the attention of engineers; but its practical application has been attended with difficulties so formidable, that hitherto it has been unattempted." From this statement it would seem that Dr. Lardner is unacquainted with the mode of gearing invented and patented by Messrs. Heatons, of Birmingham, and employed by them in their justly celebrated common-road locomotive, whose unparalleled performances have been recorded in your pages.

The statement that "such a mechanical arrangement had not hitherto been attempted," is only true as confined to railroads; on common roads the Messrs. Heatons have not only attempted, but actually accomplished all that is mentioned as desirable in the foregoing quotation. By their system of gearing, the action of the springs in no way interfered with the free and efficient transfer of power from the pistons to the driving wheels while wheels and pinions of several different sizes being employed, the power of traction, or the rapidity of transport, was capable of increase or diminution, as circumstances required. It was by means of this "mechanical arrangement" that Messrs. Heatons were enabled to skim the level roads in the vicinity of Birmingham, and to ascend the steepest hills of Warwickshire. It follows as a matter of course, that if

such an arrangement of mechanism proved thoroughly efficient, while subjected to the violent concussions of roughly-paved turnpike roads, there can be no chance of its failing under the more favourable circumstances of a railroad.

Dr. Lardner says, "but once admit the practicability of applying toothed gear, and it will be difficult indeed to say where may be the limit of mechanical possibility, whatever may be the limit which prudence may prescribe." The foregoing will, I presume, do something more than admit the practicability -it establishes the fact of its successful application_under circumstances extremely unfavourable: and I venture to predict, that when this mode of gearing is introduced into our railroad locomotives, the common results, both as to weight drawn and speed attained, will greatly surpass our present average performances.

Dr. Lardner touches very tenderly upon the " extreme caution observed by railway engineers and directors;" he admits, however, that the result of this has been to impose 66 a check amounting almost to a dead lock, on the progress of mechanical invention in this department." Whatever difficulty Dr. Lardner may feel in giving his opinion as to whether this "caution" be defensible or not, I know there are plenty of competent persons who do not hesitate to pronounce it indefensible.

It happens, most unfortunately for all parties, that although this "extreme caution" has in most cases been exercised by railway engineers towards the plans and improvements of others, they appear to have applied but little of this caution in working out their own plans and experiments. Nay, so strikingly apparent is their want of caution in this respect, as to lead to the acquirement by certain railway companies, of a considerable stock of very dearly bought experience.

On railways generally, the door has been most pertinaciously closed against almost every individual who felt desirous of ascertaining, or of demonstrating, the extent of practical utility pertaining to sundry inventions or improvements. Had more liberality prevailed in this respect, I have no doubt that many important questions, at present in abeyance-such as the safest and most eco

nomical form of boiler, the best construction and most eligible size for wheels, &c. &c. &c.-would by this time have obtained something like a satisfactory answer.

Had the ocean been no freer than railways, how many important facts would to this day have been undiscovered, how much theory would have remained unsifted. "The sea, the open sea," however, has offered an unrestricted field for the exercise of inventive genius, and the importance of the numberless experiments that have from time to time been made, with boilers of all shapes and sizes, with paddles and propellers of almost every possible variety, with every description of engine, both high and low pressure, &c. &c., the importance of these experiments, I say, may be best estimated, by referring to the present triumphant state of steam navigation.

No person, I am sure, would be found to advocate the admission of inventors to run as much on railroads, sans control, but the "extreme caution," or as less scrupulous persons term it, "the one-sided caution," is calculated to cramp the genius of skilful men, and to continue to the railway companies their present almost ruinous expenses for locomotive power.

Waiting the forthcoming explanation of the doings of the "Great Western" in "the other extreme,"

I remain, Sir,
Yours respectfully,
W. BADDELEY.

London, August 16, 1838.

FIRE ASSOCIATIONS. THEIR DUTIES POI.TED OUT.

SIR,-Permit me to thank your correspondent, Mr. P. Ober, for the flattering mention he has been pleased to make of my name at page 280, and to assure him that "the public interest" is the only object I have in view in my multifarious contributions to your pages.

I am extremely glad to find the general opinion is favourable to the advantages of Honorary Fire-brigades. I am well aware of the celebrated fire-associations of the continental towns: they have existed for many years, and it is to them we are indebted for several of the

most valuable improvements which constitute the efficiency of our present fireengines.

There is, however, one serious and too often fatal error in the working of some of these associations, which is partly illustrated by Mr. Ober, in his letter; speaking of the fire-brigades already organised in Switzerland, Mr. Ober says," In some places the members are divided, some devoting themselves exclusively to the management of the fire-engine, while others are charged with the not less important task of taking immediate possession of the house on fire, in order to carry off, and convey to places of safety, the furniture and other moveable property which it may contain. Large and very convenient bags, with which they are often provided, enable them to save also most of the minor articles, which would probably otherwise become a prey to the flames." It was a common practice, and still is in some places, a prominent object with fire-volunteers, to rescue as much property as possible from the burning building; and not only so, but even in London, up to a comparatively recent period, some of the Insurance companies maintained a corps of fireporters, whose sole duty was to rescue goods, &c. from burning buildings. At numberless fires in our own metropo lis, in many provincial towns, in America, and on the continent, the consequences of this mode of proceeding have proved most disastrous; many thousand pounds worth of property have been consumed, that would most assuredly have been preserved, had all the assistance present been concentrated upon extinguishing the flames. In Manchester, London, Edinburgh, or indeed wherever a skilful fire-police is formed, the attention is now exclusively directed to the suppression of the fire, and all the energies of the men being directed to this one point, their efforts are, nine times out of ten, crowned with extraordinary success. Where the reverse of this obtains, great efforts are often made, much property is got out of the endangered premises, and placed in fancied security a short distance off; meantime the unopposed flames are gaining such a tremendous ascendancy as to defy all subsequent efforts to arrest their

course.

The remedy being too late, is applied in vain, and the triumphant element involves in ruin all the adjacent premises, with the property originally rescued. The New York fire was a melancholy instance of this kind. Mr. Braidwood in his excellent work on fires and fireengines, very justly remarks, that “persons may often be seen toiling like galley-slaves at operations which a moment's reflection would show were utterly useless. I have seen tables, chairs, and every article of furniture that would pass through a window, three or four stories high, dashed into the street, even when the fire had hardly touched the element," and it is no uncommon sight to see glass, china, &c. precipitated from windows in like manner.

It very commonly happens that much greater risk is encountered in attempting to save goods than would be experienced in successfully combating the flames. An awful loss of life took place at Southampton, through the misdirected zeal of the volunteers who undauntedly endeavoured to bring out a stock of the most combustible description, while the most unwarrantable delay was permitted in getting the fireengines to bear upon the flames.

The removal of property in case of fire is generally of little moment, for the manner of rescue is so hurried as to damage what is preserved so seriously as frequently to render it valueless.

I should be sorry to be supposed by these remarks to forbid entirely the preservation of any kind of property; on the contrary I know there is often time afforded, and assistance at hand for saving books, papers, and property of an invaluable description, which should not be thrown away. What I wish to insist upon in all cases is, that every trained corps of firemen, whether paid or honorary, should direct all their powers to the extinction of the flames and upon no account to waste their time and labour in removing such unimportant articles as chance may place in their way.

;

This course is dictated by sound sense, and past experience fully proves its correctness.

I remain, Sir,
Yours respectfully,
WM. BADDELEY.

London, August 17, 1838.

FLAT CHAMBERED BOILERS-MR. W. HANCOCK IN REPLY TO MR. HEBERT.

In your 784th Number I find a letter from Mr. L. Hebert, in which he advocates the cause of Sir James Anderson, with that becoming zeal, which, considering the relative positions of the parties, appears to be perfectly requisite and commendable; nor does he forget to exercise the tact so common to advocates, of occupying a large space with matters of no importance to the question, and which, although easily answered, are not of sufficient weight to be worth troubling your readers about.