one-fifteenth or one-twentieth of the whole; and this rupture would release all : an explosion of the whole is impossible, because the bolts and braces by which all the chambers are held together, are of such size and strength, as to be capable of resisting a pressure twenty times greater than the chambers are calculated to sustain.

"In tubular boilers there is a confinement or throttling in the tubes, so that the steam is not freely disengaged, but goes off in gusts or starts, agitating or displacing the water, part of which it carries off with it; but in the chambers of this boiler, steam is formed and separated in a more uniform manner, the whole surface of heated water giving out its volume of steam freely, whilst the body of water is in a state of comparative quiescence.

"Mr. John Farey, in his evidence before the Select Committee of the House of Commons on steam carriages, at page 42, says'Mr. Hancock has taken the middle course in subdividing the water in his boiler, having all that can be required for safety; and the weight, I believe, on the whole to be less than that of any other boiler, which will produce the same power of steam: for owing to the freedom with which the steam can get away in bubbles from the water, without carrying the water with it, the surface of the heated metal is never left without water. Hence a greater effect of boiling is attained from a given surface of metal and body of contained water, and that with a much greater durability of the metal plates, than I think will ever be obtained with small tubes.'

"The writer believes this boiler to be superior to any that has yet been produced, whether for steam carriages on common roads, or for railways or steam-boats, and in many cases for stationary engines.

They

are lighter, take up less room, economise fuel, and are at once powerful and safe. They are also less expensive of renewal and repair. For places difficult of access they are particularly suited, as they may be taken in parts, so as to be carried by men or mules over mountains or in mining operations, and put together with facility by persons possessing little skill, as is the case also with repairs; the substitution of a new chamber for a defective one is neither difficult nor tedious.

These facilities apply equally to sea-going vessels; a spare boiler or spare chambers may be stowed in a small compass, and the means always at hand of putting in a new boiler, or replacing a chamber in the midst of the ocean at any time with comparative ease."-p. 15-17.

To proceed with the steam carriage experiments-Mr. H. thus continues :

'Being satisfied that in this boiler he had at length attained the prime requisites of a boiler for locomotive purposes, namely, great steam producing power within a small compass, and entire safety from explosion; the attention of the writer was next directed to a better construction and arrangement of the propelling machinery. Laying aside his propelling flexible engines, which he had despaired of rendering available, he determined to make those of the ordinary construction, subservient to his purpose." p. 17. His first steam carriage was one with three wheels, the power being applied by a pair of vibrating or trunnion engines to the fore wheel only, the bite of which upon the road was found sufficient to propel the carriage. Mr. H. performed journeys comprising many hundred miles with this vehicle.

"In the course of these early experimental trips, the writer experienced the usual fate of all who run counter to long standing usages and prejudices; namely, to be ridiculed by the many, encouraged by but a very few, and fiercely opposed by all whose personal interests were threatened with injury by his proceedings. The popular mind had not yet become sufficiently familiarised to the notion of dispensing with horses in common road travelling. The newspapers had made mention about this time of some private trials made by Mr. Goldsworthy Gurney, in a steam drag of his construction; but hitherto no public exhibition of anything of the sort. All had heard something of a scheme for riding by steam, but most persons with much the same degree of incredulity that we now listen to tales of journeying in the air. The writer was the first, or with the first, to offer, to all who chose to come and see, ocular demonstration of the practicability of the thing to exhibit in the face of day, and on the public highways, a carriage propelled by steam. But though this was evidence not to be gainsayed, it was not a little mortifying to see how the force of it was evaded. Some would admit frankly that the carriage worked well; but expressed as frankly their decided conviction, that it would never answer for a continuance. Others would depreciate its performances, exaggerate its defects, and exult, as it were, in every instance of accidental stoppage. If requiring temporary accommodation, through the failure of some part of the machinery,—a circumstance naturally enough of frequent occurrence in

this early period of his locomotive career, he usually experienced the reverse of kind or considerat treatment. Exorbitant charges were made for the most trifling services, and important facilities withheld, which it would have cost nothing to afford. If, again, he happened to be temporarily detained on the road from want of water, or from any other cause, he was assailed with hootings, yellings, hissings, and sometimes even with the grossest abuse. It is true, this latter description of treatment proceeded chiefly from the rabble; but he regrets being obliged to add, not exclusively so. Great obstruction was also continually experienced on those occasions from waggons, carts, coaches, vans, trucks, horsemen, and pedestrians, pressing so close on the carriage, as sometimes to preclude the possibility of moving. Altogether the writer's situation was in general anything but agreeable; often most irksome and irritating, sometimes very hazardous.

"No ways disheartened by any of these untoward circumstances, the writer persevered in his experiments; and as the novelty of such exhibitions wore off, so also did the excitement and the opposition which they at first produced Clearer-sighted views and kindlier feelings began gradually to prevail; more serious convictions of the practicability and advantages of substituting inanimate for animate power in common road travelling; and greater readiness to promote, by word and deed, the success of the project" p. 18 -20.

We shall not further follow Mr. Hancock through his various experiments and statements of the workings of his carriages. They have been from time to time recorded in our pages, cotemporaneously with their occurrence. Encountering difficulties the most severe, and obstacles the most trying, he has continued his operations to the present day from his own resources.

If any

one deserves reward or compensation from the nation it is Mr. Hancock; but we have no doubt that he would prefer that his exertions should be acknowledged rather by a company of capitalists making a fair experimental working of his carriages, and remunerating him according to their success, than any government grant to enable him to live at ease. He wants the means of activity, not of retirement. We subjoin a list of the carriages constructed by Mr Hancock.

"Steam-carriages built in the order of their construction, and the number of per

We cannot help thinking that a very fair opportunity for a few capitalists of putting the practicability of steam- locomotives on common roads to the test here exists. It certainly would not cost a great sum to put these carriages already made into complete repair, and to place them on some moderately level road, between London and some town about twenty or thirty miles distant, where there is good passenger traffic. Let them run constantly at particular intervals each day for a certain time, say three or six months. A correct account kept of the receipts and expenses of this traffic would certainly set the matter at rest. We hardly think that less would satisfy the public. The difficulty which Mr. Hancock has now to overcome is greater than those he encountered seven or eight years ago. He has now to overcome the indifference of the public. The subject has been so long on the tapis, that a steam carriage on the streets is looked at as a passing show, and then dismissed from the observer's mind. The eagerness which follows a first experiment has passed off, and as those who were zealous in the onset have not succeeded, it is considered as a settled thing that the project never can succeed.

The following estimate appears in Mr. Hancock's work:

-

"The estimate of expenses and wear and tear has been calculated from the actual working of the writer's steam-carriages during their running for hire on common roads, but principally from the "Automaton,' this carriage being the only one he has hitherto built of sufficient magnitude to cope with the ordinary contingencies always to be found on a long line of road. To this estimate the writer has added another, showing the outlay necessary for an establishment on a large scale, and the probable pecuniary results.

ble of greater efficiency than that of low pressure steam; firstly, because owing to its higher temperature its volume is not diminished to the same extent that its pressure is increased; and secondly; because the friction attending its operation not being increased in the same ratio as the pressure, the available force, or excess of the pressure above the friction, is relatively greater than that of low pressure steam. High pressure steam, then, is in every respect capable of greater efficiency, and if we find that a given weight of high pressure steam can be propagated with the same expenditure of fuel as an equal weight of low pressure steam, we may look for the most beneficial results from its employment, expansively, in steam navigation, as well as in all cases where economy of fuel is of vital importance.

But here I shall be met with an exclamation against the danger of employing high pressure steam. Now my opinion is, that little or no increase of danger would ensue from its adoption, because there is no reason whatever why a high pressure boiler, if made proportionably stronger, should be more liable to burst than a low pressure boiler; and as to the effects of an explosion, if from the greater efficiency of the steam, and the consequent reduction in the quantity required, we should be enabled, as I believe we should, to reduce the size of the boiler in nearly the same propor tion that we increased the pressure of the steam, the consequences of an explosion would probably not be more dreadful than at present.

It is to be recollected also, that the mere reduction in the size of the boiler would itself tend to increase its strength, or more correctly speaking, to diminish the aggregate pressure it would have to sustain, and would also lessen the risk of the occurrence of defective parts in its material and construction, and so contribute to increase its safety. And here I may observe that the reduction in the size of the boiler would be more than proportionate to the reduction in the consumption of steam, because that part of the boiler which is occupied by the steam, and which is usually about one-third of the whole, would be reduced in a double ratio,-first in proportion to the smaller quantity of steam it would have to contain; and secondly, in proportion to the greater density of

that steam. Nor would this further reduction in the size of the steam chamber in respect of the greater density of the steam, have any tendency to render the priming of the engine, as it is technically called, greater than at present, because the violence of the ebullition in the boiler would also be diminished in exactly the same degree that the density of the steam evolved from the water was increased. If, however, after all, boilers of the common construction could not be relied upon for steam of excessive pressure, tubular boilers might be substituted, the bursting of which can never occasion very serious mischief. Tubular boilers no doubt have their disadvantages, but would those disadvantages outweigh the enormous benefit to be derived from high pressure steam?

With respect to the relative consumption of fuel in the propagation of high pressure steam, it is now perfectly well ascertained that the quantity of heat required to produce a given quantity, or weight of steam, or in other words, to evaporate a given quantity of water, is always the same, whatever the density of the steam may be, for where the sensible heat is greater, the latent heat is less in the same degree, and vice versa. Unless, therefore, there be some increased practical difficulty in the way of communicating the heat to the water, it is clear that the efficacy of the fuel would not be impaired by increasing the pressure in the boiler, and that whatever saving might be effected in the consumption of the steam by increasing its pressure, would be attended with a commensurate saving of fuel. Whether or not any greater difficulty would be experienced in communicating the heat to the water would be best proved by experiment, but I shall here briefly state my reasons for believing that such increased difficulty would not occur, or at least not in any material degree.

The rapidity with which the heat of an engine furnace is communicated to the boiler, depends upon the disparity between the heat of the furnace and the temperature of that part of the boiler which is in contact with the fire, so that the heat of the fire being the same, the hotter the boiler, the less, in something like the same ratio, will be the quantity of heat communicated to it.

Now the quantity of heat communi. cated to the boiler is, of course, a mea

sure of that which is transmitted to the water, so that we have only to inquire what effect the increase of pressure would have on the temperature of the boiler, to determine the difference in the quantity of heat which would be transmitted to the water. In the first place, then, the mere increase in the temperature of the water consequent on the greater pressure under which the steam might be generated would not add sufficiently to the heat of the boiler to produce any sensible approximation to that of the fire, so as materially to impair the efficacy of the fuel.

The only question then is, whether the part of the boiler in contact with the fire would be more liable than at present to acquire a temperature greatly exceeding that of the water within? Now, so far from this being the result of increasing the pressure, I conceive the very reverse would be the case, because since the steam produced in the boiler would be of greater density, and consequently of smaller volume, its formation at the inner surface of the metal through which the heat was transmitted to the water would displace the water to a less extent, and so render the contact of the water with the metal more perfect than it can be in a low pressure boiler. If it were necessary to increase the thickness of the boiler in order to give it the requisite degree of strength, that circumstance, no doubt, would have a tendency to cause the part of the boiler which was exposed to the fire to become unduly heated; but a boiler may be made of any degree of strength, without at all adding to its thickness, merely by multiplying the number of internal stays from side to side.

With regard to the greater loss of heat by the radiation of a high pressure boiler, that is a matter of very sinall importance, for by surrounding the boiler with a case of non-conducting material, the radiation may be reduced to a very trifling amount.

On the whole then, I can see no substantial objection to the introduction of high pressure steam, so far as its propogation is concerned; and now let us turn to the practicability of employing it expansively.

As far as I can see, the only appearance of difficulty which presents itself in this quarter, is to obtain an equable

result from the varying force of the expanding steam. In pumping engines, as in those of the Cornish mines, where the expansive principle is adopted with such great advantage, this varying force is exactly what is wanted; but where a continuous uniform effect is to be produced, some means must be had recourse to for amalgamating the greater with the weaker force of the steam. Α heavy fly-wheel is the usual expedient for attaining this object in expansive engines, and where the steam is not cut off at a very small portion of the stroke, it answers the purpose sufficiently well. But in steam vessels this method would be extremely inconvenient. In reality, however, marine engines as now usually constructed, do already possess the means of greatly equalizing the varying force of the steam when used expansively. For, where two cylinders are employed, as is almost universally the ease in such engines, each receiving its steam at half the stroke of the other, the difference between the greatest and least mean pressure on the two pistons taken together, no matter at what part of the stroke the steam may be cut off, would only be one-half as great as the difference would be per square inch, if only one cylinder were employed. And if the steam were cut off at a very small portion of the stroke as at one-fourth or one-fifth, its power would be still further equalized by the operation of the cranks, which is the very reverse of their effect where the pressure of the steam is uniform.

pro

The force thus obtained from two cylinders worked expansively would bably, with the assistance of the impetus of the paddle-wheels, be sufficiently uniform even to allow of the steam being cut off at so small a portion of the stroke as one-fourth or one-fifth; but if it should not be so, the addition of a third cylinder, adapted to act in proper rotation would, I think, produce the desired effect beyond a doubt.

If other practical objections do really exist, either to the propogation of high pressure steam, or to its employment expansively, I can only repeat, that the advantages to be derived from their removal are so enormous, that if they be not palpably insuperable, the most strenuous exertions ought to be used to subdue them. For my own part I am