moving power, as it were, renewed as often as should be necessary, instead of operating only from the end; while the effect of exhaustion was to diminish instead of increase friction; as these things were evident, I was careful, both in my patent and my pamphlet, to disclaim any exclusive right to the method of operating by a plenum; or blowing air in behind the carriage. Mr. Medhurst has, therefore, the claim of originality of invention, to whatever benefit may result from operating by a plenum, or moving a vehicle in a tunnel, by air pumped in behind it; as I not only disclaim the process, but also proclaim that it will not do.

But these are not the only distinctions between my proposition and that of Mr. Medhurst: the " arrangement without which the operation of the principle would even be attended with doubt, delay, and danger," that is, "the new mode of telegraphic communication, described in the last section of the treatise, which, being equally efficient during the most foggy weather and darkness, as in day-light and clear weather, will admit of instantaneous communication between those who direct operations at each end; so that any thing it may be necessary should be known at one end, may be instantaneously communicated from the other, independent of the method of conveyance itself," being a third distinguishing feature.

Blind, however, to all these things,' the notorious dealer in falsehood and calumny to whom I have alluded, but whose name shall not sully the page, has had the audacity to charge me, by statements in the public papers, and various prospectuses (which I hold, and shall produce as evidence in the action I have been advised to commence against him) with pirating the idea, first from himself, and then, when he found that ground untenable to a degree which induced even him to abandon it, from Mr. Medhurst. It became necessary, therefore, to point out the distinction between the two propositions; and having done that, I will advert to the circumstances, which cause me to say, that whatever benefit may arise from operating by a plenum, Mr. Medhurst will deserve the credit of it.

"The rate at which a fluid will rush along a pipe, depends on the pressure operating upon the fluid, and its friction against the pipe. The friction of a fluid against a pipe, increases with the length of that pipe. Let the velocity with which a fluid would rush along the part of the pipe it first entered, be what it might, provided the pipe were long

1 Page 34 of a certain Letter to Dr. Yates shews, however, that there is one other person at least equally blind.

enough, friction would increase sufficiently to reduce this ve locity to almost nothing. A circumstance which occurred some years ago, is conclusive on this particular. It is too well known, to be at all affected in point of veracity, by an inability to mention either the exact time or place, that the proprietor of an iron work in Wales, had, some years ago, occasion to erect an additional furnace at the distance (recollection states) of about three-quarters of a mile from his old ones. The blast apparatus of these old works being large enough to supply this new furnace in addition to the old ones, he conceived it would prove much cheaper, if, instead of having power and blast cylinders erected at the new work, he were to lay a pipe from the old ones, to convey to the new one the superfluous blast. This he accordingly did; and as soon as the pipe was completed, set the apparatus going, to ascertain the strength of the blast he could thus apply to the new furnace. To his great surprise, however, no blast was produced; a gentle current, which would not blow a candle out, being all that was perceptible. For a result so adverse to his expectation, he could account in no way, but by supposing that from accident or design, the pipe was stopped up. As the readiest way to ascertain whether it was so, he put a cat in at one end, and blocked it up, leaving her to find her way to the other.

"The pipe, though large enough to allow her to move forward, not admitting of her turning round, puss had no alternative but that of seeking an exit at the other end: this she accordingly did, and, contrary to his expectations, soon made her appearance there. Convinced by this, that there was no obstruction in the pipe, he concluded, that the disappointment he had experienced arose from the friction of the air against it; and finding that he could in no way obviate this difficulty, he was obliged to throw the pipe aside, and be at the additional expense of blast apparatus for his new furnace.

Now, had the proposition this treatise submits been, that we should convey ourselves throngh a cylinder such as has been adverted to, by employing apparatus on the principle of blast furnaces, to blow us through, by forcing air in behind us, the circumstance which has just been stated would be fatal to that proposition. But when, instead of being blown through, by air forced in behind us, it is proposed to cause the air which is behind the vehicle to operate to push it forward, in consequence of some being taken from before it, the case is widely different. Air which is forced to move in a pipe, in consequence of other air being driven into that pipe behind it, operates as a wedge, and opposes to the power which moves it, resistance arising from becoming, as it were,

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of water, and 0. 6 inches of water; and if we conceive that forcing air to move in this way, is in some degree analogous to drawing an elastic, endless rope, the size of which should be equal to the larger end of the pipe, through it, and out at the smaller end, we may form some idea of the degree to which power would be absorbed in operating by a plenum. And not only this; since reversing the operation, and supposing the rope to be drawn from the smaller to the larger end, will also give us some idea of the effect of operating by exhaustion, or vacuum; and enable us to conceive that "air which is allowed to move, owing to some being taken out from before it, instead of being forced in behind it, becomes affected, as any thing from which a wedge is withdrawn, is affected; that is, freedom of motion is allowed, and its parts play so much more freely, that friction is diminished instead of increased."

And as every additional 56 feet (or doubling of its length), that might be added to any pipe through which air was forced as from bellows, would double the pressure, it may easily be conceived that increased friction would cause increased condensation, and increased condensation again increased friction, till the effect became realised which the proprietor of the iron works experienced.

From not being aware of this, the results Mr. Medhurst draws are erroneous to a degree which causes him to state that the density of the air would be increased only the 77th part; whereas it would be doubled; and owing to the pressure being eccentric instead of concentric, the tube, or "canal" he proposes, would be blown to pieces; while the power required would be fifty times greater than he states. It is true, that his error is increased by calculating according to the rule of simple proportion, after he has laid it down as an axiom that "in different degrees of velocity, the resistance by friction will be as the square of the velocity:" but the fatality pervades the foundation as well as the superstructure.

Having thus cursorily adverted to the distinction between what I propose, and for which I have obtained a patent, and what Mr. Medhurst proposed in 1812 and stated himself to have a patent for, notwithstanding the records of the Court of Chancery prove such statement to be contrary to fact, I conclude by saying, that I knew not, until after my own patent was obtained, that the idea had ever been thought of by any one besides myself: though I have since learned, not

1 The limits of the page render it necessary that the scale of length should be in hundredths of an inch, but as the width would have been imperceptible had the same scale been observed, tenths are adverted to for it.

only that Mr. Medhurst, but many others had thought of it; and I find the principle of transmitting power, or rather imparting an impulse by means of a vacuum produced by air pumps, to have been operated on by Papin nearly 150 years ago. My patent, however, being, not for the principle, but for the combination of the valves, telegraphic apparatus, &c. &c., is no more affected by this, than my judgment is by charges relative to non-originality of invention--since, in neither my patent nor my pamphlet, do I assert originality; though I believe myself to be the first who ever worked (or carried) the principle through, even in theory, independent of reducing it to practice.