struction of the machine, were perfected with a skill and accuracy till then unknown in the execution of large machinery."

"But this is not all. In Philip's History of Inland Navigation, it is stated, that when the first canal cut in England "was completed as far as Barton, where the Irwell is navigable for large vessels, Mr. Brindsley pro posed to carry it over that river, by an aqueduct, thirty-nine feet above the surface of the water in the river. This, however, being considered as a wild and extravagant project, he desired, in order to justify his opinion towards his noble employer, that the opinion of another engineer might be taken, believing that he could easily convince an intelligent person of the practicability of the design. An engineer of eminence was accordingly called, who, being conducted to the place where it was intended that the aqueduct should be made, ridiculed the attempt; and when the height and dimensions were communicated to him, he exclaimed, I have often heard of castles in the air, but never was shewn before where any of them were to be erected.' This unfavourable verdict did not deter the. Duke from following the opinion of his own engineer. The aqueduct was immediately begun, and it was carried on with such rapidity

N

and success, as astonished all those who, but a little before, thought it impossible; and within twelve months did the crews of the vessels navigating the Irwell, see the Duke's barges sailing over their heads, in the channel upborne by this castle in the air.'"

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"Now had it happened that, because these engineers, who were both (more particularly Smeaton) men of great eminence, did not see how the difficulties incident to the respective cases could be overcome, those who supported Watt and Brindsley in their attempts, had withdrawn that support, because great names pronounced the objects they were aiming at "impossible," had this happened, could the President of the Board of Trade have had to say, "But I cannot help stating, that on looking back to the contest in which we were for the last quarter of a century engaged, it is not too much to say that we are mainly indebted to the new resourees furnished us by Mr. Watt, for the manner in which we brought that contest to a conclusion; or the First Lord of the Treasury been commanded by his Majesty to state, "That he feels deeply sensible of the merits conferred on this country, by the individual to whose memory we are now about to pay a tribute of respect and gratitude; and that his Majesty is most anxi

ous to place his royal name at the head of the proposed subscription, for the sum of £500."

"And yet is there nothing one whit more difficult than (nor indeed so difficult as) what Brindsley and Watt accomplished, in the object here proposed. But even though there were, would that be any reason to despair of effecting it? There are others, beside him on whom has devolved the duty of advocating it, who see it practicable. And is it to be supposed, that their perceptions are more acute than those of their countrymen? They but too deeply feel the contrary; well knowing, that if public attention could but be so turned to it, as to cause our men of science to give it consideration, difficulties would disappear as fogs from before the sun."

The proportion in which future times shall acknowledge that the sun of your intellect contributed to disperse the clouds by which public perception on the subject is at present obscured, I leave to yourself to decide.

I am, Sir,

Your most obedient Servant,

JOHN VALLANCE.

APPENDIX.

It may be as well to take advantage of the necessity which has been imposed on me, of rectifying mis-statements of one sort, to rectify those of another description. For purposes of the basest kind, a well known character has chosen to charge me with pirating an idea broached some fifteen years ago, by a Mr. Medhurst. To set this question at rest, it will be only necessary to shew the difference between the two propositions.

It appears, that in the year 1812, Mr. Medhurst published a tract, recommending the transmission of persons and goods through a square tube, by air forced into the tube as from a pair of bellows, i. e. by a plenum; instead of by exhaustion or vacuum. To this tract he put his name as Patentee, notwithstanding that the records of the Court of Chancery prove he never had any patent for it.

When I first took up the investigation, I knew not that it had ever been thonght upon by any one: and the way in which the idea first presented itself to me, was to operate by a plenum; and force air in behind the vehicle, as from bellows. But on entering into the calculations which became necessary, as soon as I had ascertained we had the means of rendering the principle practicable so far as related to the construction of the tunnel, the air pumps, and steam-engines to work them, I found that the friction of the air, would absorb power to a degree that would render this method of operation utterly impracticable.

In consequence of this, I turned my thoughts to operating by a 66 instead of a vacuum, plenum;" and to rendering the atmosphere the motive force, by exhausting from the tube instead of pumping into it; and as it was evident, that by arranging valves at every mile, or half mile, as experience directed, which the vehicle should open as it passed over them, air might be admitted where we pleased, and the