rious accounts and calculations in proof of his several positions are appended to this report of Mr. Brunel, and an estimate that to carry on the works as he recommends, the sum of 94,000l. will be required during one year from August, 1837.

The Lords Commissioners of her Majesty's Treasury having refused their assent to the tunnel being begun on the Middlesex side, Mr. Brunel in his report, dated the 7th of September, 1837, repeats the other re commendations of his former reports.

The last report of Mr. Brunel that is referred to me is dated the 15th of November, 1837, the fourth irruption of the Thames having taken place on the 2nd of that month. In this report he considers the third irruption (that of the 23rd of August) as not having been unfavorable in one point of view, as it would enable substantial ground to be substituted for the loose silt that had been worked into the tunnel by the irruption, in proof of which he states that the work done before the third irruption cost 900l. per lineal foot, while what was done between the third and fourth irruptions cost only 6301. The former recommendations and arguments are repeated, and in addition it is now stated that the fourth, or last irruption, was caused in a great degree by the part of the tunnel then in progress being under the portion of the river chiefly used for navigation, and that the depth being small, the artificial bed of the river, or roof of the tunnel was liable to be disturbed by passing vessels. This Mr. Brunel now proposes to remedy by deepening a part of the river where the tunnel is formed, moving some of the ships in the tiers near the tunnel from the northern to the southern side of the river, according to a plan which accompanies his report, throwing the space which is required to be kept clear for the navigation, from the north side towards the middle of the river over where the tunnel is formed, so as to leave the space which is in advance of the works free for tunnelling operations, and then substituting a thicker roof of clay and gravel raised above the present level, to which, from the navigation not being then over that part, there would not be the same objection as at present. This thicker roof Mr. Brunel proposes to make 100 feet in length, or in advance of the shield, and 100 feet on each side of it. He calcu lates on a great saving in the end from this artificial covering, which he estimates at 1,8007., and ascribes much of the late trouble and expense to the passing ships, and the want of a sufficient thickness in his roof, which the navigation prevented his having.

The reports are drawn up in great detail, and the above abstract is to be considered not as a substitute for them, but only as bringing the leading points to recollection in

one view, without the repetitions which the reports themselves, being of different dates, naturally contain.

It is now my duty to state my opinion, which is, to recommend Mr. Brunel's proposals to be adopted, as the most economical and creditable way of executing the works, if it be the determination that the Thames Tunnel (a work which for many years has attracted much of the public attention in this, and still more in other countries, and upon which upwards of 80,000l. of public money has been advanced) shall be completed, without making cost an element in the question. I would then even advise more effectual works in front of the shield than Mr. Brunel's description and estimate of 1,8007. contemplates; for if the work is to be considered a national or Government work, a repetition of the danger, the late irruptions, and the enormous expense of the work, would be discreditable, and as it may be, it ought to be prevented. In addition to Mr. Brunel's proposals, I would recommend, after the removal of the clay that has lately been thrown in, and a portion of the silt, that two rows of close whole timber piles should be driven between where the ground begins to rise and the present shield, one row on each side of the line of the tunnel, with space between sufficient for the shield to travel, and to as great a depth as they can conveniently be driven, the heads being level with low water. These, with a return of shorter piles at the end, would form a dam against the silt. The piles being driven, I would continue the dredging of the silt in the space enclosed by the piles, and then fill up with clay, gravel, &c., as at present, to a sufficient height, and afterwards give the mass time for consolidation before attempting to advance the shield, which in my report to the commissioners for the loan of Exchequer-bills, I stated to be an essential element for success in the undertaking. In the progress he has made through very bad strata, Mr. Brunel has fully tried and proved the great power of his excellent shield; but the strata, rendered worse by the irruptions and the causes assigned by Mr. Brunel, are now too bad for even the shield to overcome. By the substitution of good artificial soil to work through, and keeping the silt or sand back by the piles, there would be much less difficulty or danger; and with proper precautions, my decided opinion is, that the tunnel may be completed notwithstanding the late irruptions, and with comparatively little difficulty or risk.

Here the question naturally presents itself, at what cost? and to answer it with the probability of accuracy is still very difficult.

The amount of the company's ca-
pital expended previous to any
advance of public money was
180,000. On the 27th of Feb-
ruary, 1837, when (64,6007.) re- 64,600
ceived from the Commissioners
for the Loan of Exchequer-bills
had been expended, I estimated
the addition then required to
complete it, at.....

Making, exclusive of the com-
pany's capital......

310,600

£374,000

Between the 27th of February and the 2nd of November, 19,3007. have been expended, making 83,9007. of public money expended to the 2nd of November, but the quantity of work done with the above 19,3007. is only 19 feet six inches, making (inclusive of 1,4007. for pumping, excavating, and claying, after the third irruption), nearly 10007. per foot, which very much exceeds all previous estimates, and proves what I stated in evidence before the Select Committee of the House of Commons, that no prudent man would commit himself to the accuracy of an estimate of this work, while it shows also the impolicy of attempting to drive on the shield through the present bad soil without a sufficient covering and time for consolidation.

In the present situation, I consider that the sum of 150,0007. should be taken as the estimate for completing the tunnelling; and that the shafts and other works remaining to be done, together with the purchases, should not be estimated under 200,0007., making, with the 84,000l. of public money already expended, and the company's capital previously expended, a total of 614,0007. for the estimate of the work, or upwards of triple the original estimate, and this is allowing but a moderate sum for contingencies, WHICH

HAVE HERETOFORE BEEN VERY HEAVY.

I have estimated the great descents at double Mr. Brunel's estimate, and yet I have, from the nature of the work, as much doubt as to the sufficiency of that sum as of any other item in my estimate.

If, however, in place of determining to complete the tunnel without reference to cost, which the foregoing observations suppose, the Lords of the Treasury resolve, as heretofore, to confine their operations to the advance of the tunnel, so as to remove any doubt of its getting through, before they sanction a further heavy outlay, then, although I agree with Mr. Brunel that the pumping-well or the shaft with the drift-way or drain would lessen the springs, I do not by any means think them so essential to the progress of the work as to agree in recommending their being proceeded in at present. Up to the time of the second irruption, in

January, 1828, the works were under the uncontrolled management of the directors and engineers, and during that period nothing had been done on the Middlesex side with a view of draining the water from the tunnelling, although it had been advanced to the middle of the river, only 155 feet having been done since; but in the report of 1831 the drift-way or adit is proposed and estimated, with the pumping-well, at 6,0002. Mr. Brunel informs me that the drainage in the tunnel is now very small, and the short time in which the water, after irruptions, has been taken out, proves that the present pumping-engine is fully equal to the work.

More rain by two inches fell during the last six months of 1836 than of 1835, an increase, but not such as to cause a very important difference in the workings, which I ascribe almost entirely to the ground towards the Middlesex side being of a looser and more sandy and silty nature than towards the south side; this, it has always been said by the Trinity officers and others acquainted with that part of the river, would be found to be the case; so that, although the spring-water has been an evil and an hindrance, the Thames water has been another and probably a greater, and is the present enemy, which makes the cases of the London Dock or the Kilsby Tunnel parallel to a certain extent only. It is not in preventing the communication with the spring, but with the river water, that the artificial roof of clay, &c., has been useful.

I agree that the air for respiration would be improved by the drift-way, and probably the present air-pump, which is worked by the steam-engine, rendered unnecessary; but this pump, ingenious as all Mr. Brunel's applications are, appears to completely answer the purpose, and would probably be found quite as effectual in abstracting the sul phurated hydrogen as a drift-way at the bottom would be.

I cannot agree as to the saving of expense by the shorter distance to the Middlesex shaft; the difference of distance in the present situation of the shield would be only 70 yards, and as an excellent railway is laid, and machinery attached for working it by the steam-engine, I am sure that the conveyance of the excavated soil along the bottom of the tunnel to the low ground on the Surrey side must be at least as cheap as to the Middlesex side, where the ground is chiefly covered with buildings, and does

*The quantity of rain that fell in the last six months of 1835 (as kept at the Royal Society's Rooms) was 104 inches, and in the corresponding In the same peperiod of 1836 it was 12 inches. riod of 1834, a very dry year, it was only six inches.

not require to be raised, and that, as a pas sage to and from their work, the workmen would generally prefer the spacious lighted tunnel to a drift-way until the difference of distance is much greater than at present.

That the well or shaft on the Middlesex side would give employment to the miners and other workmen when they cannot be employed in the shield, and thus lessen the amount now charged to the tunnel, I entirely agree; but my opinion at the same time is that they may be fully employed in securing the ground in advance of the shield, according to Mr. Brunel's plan, or with the additional piling, such as I have suggested. It ap pears to me that sinking the shaft, driving a drift-way, making a new shield, and proceeding from the Middlesex side, would amount to a committal to go through with the undertaking, and ought not to be begun until that, as a previous question, has been determined.

In stating this, I am in some measure influenced by the opinion that Mr. Brunel's estimate for the works on the Middlesex side is too low. He estimates the pumping-well and drift-way at 7,0007., and the shaft-engine and pumps at 6,8447., and gives a decided preference to the shaft. Now, the shaft on the Surrey side is stated in the account to have cost 20,000l., and evidently the driftway, 4,3107., should have been added to the shaft as to the well plan. The Middlesex shaft may, and probably will, be less expensive than the Surrey one was; I think it unsafe to trust calculation against experience, so far as to take one-third of the actual of the Surrey as the estimate for the Middlesex shaft.

Of the propriety and importance of changing the channel for the passage of vessels, from the part of the river in front of the shield which has yet to be tunnelled through, over to the part which is tunnelled, and forming a body of compact gravel and clay in front of the shield, in the way Mr. Brunel proposes, to a greater thickness than is now compatible with navigation, there can be no question; and I am glad to learn, by a letter received from Mr. Charlier, that the Navigation Committee have agreed to the proposal, and as Mr. Brunel considers that this will remove much of the cause of the late irruption, by enabling him to have a better covering of clay, and preventing vessels grounding upon the artificial bed, and estimates the necessary work at only 1,8007.,

I have no hesitation in recommending to the Lords of the Treasury to sanction it, even with the addition I have proposed, should Mr. Brunel be disposed to adopt it. I think the expense of the piling and clay may be taken at about 10,0007., and I feel assured that, if the completing of the tunnelling be the object, this outlay will be more effectual, and much less in amount, than proceeding with the works on the Middlesex side; from the length of the river proposed to be covered with clay, if done according to Mr. Brunel's plan, being three times greater than with piling suggested by me, I think the difference of expense of the two plans would be small.

Having now given my opinion on the various points that have been referred to me, I would beg to add, that as the Thames Tunnel is Mr. Brunel's work as respects design and responsibility, any measure that may be proposed for executing the work should, in my judgment, have his approval. If that approval is refused, unless the Lords of the Treasury will consent to works which exceed the amount they have yet thought proper to agree to, almost any course would be better than letting the complaint be repeated, "that the engineer has been deprived of the proper means of completing the work at the estimated cost."

December, 1837.

JAMES WALKer.

LIST OF IRISH PATENTS GRANTED IN JUNE, 1838.

John Melville, of Upper Harley-street, for improvements in the generation of steam, and propelling vessels by steam or other power.

Alexandre Happey, of Basing-lane, London, for a new composition applicable to paving roads, streets, terraces, and other places, which improvements are applicable to the different purposes of building, and also in the apparatus for making the said composition.

Ambrose Ador, of Leicester-square, for improvements in lamps or apparatus in producing or affording light.

Pierre Armand Lecompte de Fontainemoreau, for improved methods of preventing the oxidation of

metals.

Ambrose Ador, of Leicester-square, for improvements in producing or obtaining motive power.

Railway Map of England.-On the first of August will be published the Title, Index, and Contents to vol. 23 of the Mechanics' Magazine, and as a frontispiece to the volume a large map of the Railways in England and Wales, price 6d. The map alone on fine paper, price 6d. Also the volume complete, in half-cloth, price 8s. 6d.

HUNTER'S MACHINE FOR CHAIRING

AND BORING RAILWAY BLOCKS.

Mr. Hunter, of Leysmill, Arbroath, whose ingenious stone-planing machine was described in our Magazine for Oct., 1836, (No. 636,) and which has since that time continued to work with com

plete success, has lately invented and patented a machine for cutting out in stone railway blocks, the beds for the reception of the chairs, and for boring holes to receive the wooden pins into which the spikes are driven, by which the chairs are fastened to the blocks.

We shall proceed to describe the machines, and afterwards make a brief mention of the success which has attended their operation. Now that it appears to be a question amongst railway engineers, whether stone blocks or wooden sleepers are most worthy of adoption, whatever may tend towards the economical formation of either the one or the other, must be of interest to all connected with this novel and important branch of inland transit. Taking this view of the matter we shall be explicit in our description, and careful as to the authenticity of the statements of working which we publish. The principle of action of the cutting tool, in Mr. Hunter's boring and chairing machines, is precisely similar to that of his planing machine, and its application in the present instance is most ingenious. Fig. 1, is a front elevation of the boring machine; fig. 2 an end elevation; and fig. 3 a ground plan and top section through the line A B of figures 1 and 2. SSSS is the framework of the machine, consisting of four iron uprights and connecting pieces. The top-piece E, composed of two somewhat flexible plates of iron, by having semicircular bends atoo, clasps the boring tools K1 K2, and holds them firinly at the height at which they are placed, by the screws N', N2, N3. MI M2, fig. 1, are augers of a spiral form, which instead of having centre-bits like the common auger, terminate in two broad-faced points, turning in opposite directions. L'L' are male screws, into sockets in the lower ends of which the heads of the augers M1 M2 are inserted and secured. K1 K2 are female screws or sheaths, into and through which the male screws L'L2 work. The winch or cross-tree R, being placed upon the head of either of the

screws L1 or L2, on being turned, works the auger. G is a railway truck or carriage, for conveying the stone block which is to be perforated, under the boring tools; and HH the rails on which the truck runs. The sheaths K1 and K2 are fastened in the head-piece E, at a height corresponding to the depth of holes required to be bored in the block, by the screws N1 N2 N3.

On examining this arrangement it will be seen, that on the tool being turned, the points of the auger must scoop out or chip off at each revolution a portion of stone, as great, at least, as the distance the screw has descended. Thus, there is no scraping action, (in all hitherto invented stone-cutting machinery found so destructive to the tool,) but, as in the stone planing machine, pieces or chips of stone are removed by the great and steady power applied to the tools. Were the thread of the screw which regulates the descent of the tool very fine, or were the augers merely kept pressed against the stone by a weight or spring, (as has been hitherto tried,) the tool would merely grind away the stone, and at the same time its own edge; but by Mr. Hunter's arrangement the stone must either yield to the descent of the auger, the rate of which is to an extent incompatible with a grinding action, or the tool must break. The chips ascend through the spiral channel of the auger, and are thrown off at top.

The chairing machine is somewhat similar, in general construction, to the boring machine. Figs. 4 and 5, (see our front page,) are front and end elevations. Fig. 6 a ground plan and top section through the line AB of figures 4 and 5. SSSS the framework. The top crosspiece E, is of the form shown in the top section, fig. 6. Z is a sheath, plain on the outside, but tapped through the centre with a female screw, inserted in the top E, and with broad shouldered pieces SS, having orifices ee, so that when the long tails m, of the pins zz are passed through these orifices, the said long ends pressing against the sides of the crosshead F, fix the sheath Z in its position, and prevent its turning. T is a male screw, which works in the female screw of the sheath Z, and has a cross-piece fixed to its lower extremity, the two arms of which carry the tools or chisels U W and UV. Y is another male screw which