PROGRESS OF THE THAMES TUNNEL.

As there now appears to be some likelihood of the completion of Mr. Brunel's

great bore," we have thought that a statement of its late progress would be interesting to our readers; we, therefore, subjoin the substance of the last Report of the Directors to the hope-sick Proprietors, at a meeting held on the 7th of September last.

The Directors state, that since Midsummer last, "60 feet of the brickwork of the tunnel have been completed, which added to the quantity previously finished, makes a total of 660 feet. By this addition the tunnel is now carried beyond the centre of the river, and is steadily approaching the Wapping shore."

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After reminding the Proprietors that the stoppage in 1828, was occasioned by no difficulties of an engineering nature whatever, but solely on account of the original capital of the Subscribers being exhausted," and that at that time about 599 feet out of 1,300 feet, which is the extreme length of the horizontal roadway and the shaft, were completed for the sum of about 120,000l. only" they proceed with statements more immediately interesting, because they relate to the late progress and present state of the works :

"In their annual Reports of 1835 and 1836, the Directors endeavoured to guard against an undue expectation of progress in the first year, and they did so from three distinct considerations:-They were assured by the Company's engineer, Mr. Brunel, that to remove the old shield and to replace it with a new one would be a work of great expense, of slow progress, and of great danger. The expense, however, is one properly chargeable upon the whole work to be done, and must not be considered as exclusively belonging to that which has been recently completed. They were aware also from experience, that when this hazardous work was effected as it was with unexampled skill and presence of mind, that the knowledge of a vast and complicated machine, and the mode of working it, could only be acquired slowly, and that hence delay in the rate of progress was incidental to the recommencement of the works, and was to be expected for some time afterwards. Added to which, these difficulties were to be encountered under the deep part of the river, where its bed was known to be most unfavourable to the labours of the miners, and most susceptible of the fluctuating influence of the tides. Notwithstanding these difficulties, the tunnel has advanced to

the extent already mentioned; and though they have retarded the progress of the work, yet the miners have acquired both confidence and familiarity in the discharge of their duties and in the management of every part of the shield, and hence it may be fairly anticipated that when the deep part of the river is passed, and where none of the greater difficulties of the undertaking may make speed of less importance than safety to the men and security to the works, a quicker rate of prògress will become practicable.

"To enable the Proprietors now to form an opinion of the state of the works, the Directors submit the following details under distinct heads, which are in substance the weekly Reports of Mr. Brunel to the Directors:

"1st. The New Shield has fully answered its purpose, and has enabled the work to proceed through some portions of ground in almost a fluid state. It is greatly superior to the old one. The resistance against which it has to exert its power is computed at about 3000 tons, vertical and lateral pressure; nevertheless, it possesses both facility and precision of movement. Some idea may be

formed of the extent of the excavation which it enables the miners to carry on through ground of the consistency previously described, and which it preserves until the brickwork is completed, when it is known that the whole area of the ground is equal to 2000 superficial feet, over the whole of which vents are opened for the infiltration of water both from the river and land-springs, which latter have been found most copious, and sometimes a source of considerable alarm and difficulty. The total area from over which such vents are opened, and through which infiltration takes place, exceeds 75,000 superficial feet.

"2d. The Reservoirs and Drains, lately completed, have under the largest influx of water given facilities to the progress of the miners unknown before. Formerly forty handpumpers, in gangs of twenty each, besides artificers in conjunction with them, were required, who greatly impeded the miners and bricklayers, and who, owing to the adoption of the reservoirs and drains, are now dispensed with.

"3d. State of the Ground.-On the suspension of the late works, a temporary covering of made ground was raised over and around the head of the tunnel, consisting of gravel and clay; but in consequence of the long cessation of the works, the City Authorities ordered this covering to be removed, in order to restore the navigation of the river to its usual state, which was accordingly done. Upon resuming the works, and on examining the ground, the favourable state of it enabled the engineer to proceed for a time without again resorting to the protection which it

afforded; it was, however, thought prudent to obtain from the Lord Mayor permission to resort to this plan when necessary, as a precautionary measure against the great influence of the tides whilst the tunnel is being constructed under deep water. The influx of river-water is discovered by its temperature, as well as by the increased quantity pumped up by the engine, and it is found invariably that a timely resort to this expedient immediately reduces the quantity and brings it under control. The precaution is, therefore, one essential, in the opinion of the engineer, to the security and progress of the works.

"4th. Rate of Progress.-Since the annual meeting, 60 feet of brickwork have been completed which, added to the 10 feet (always occupied by the shield) excavated, makes a total of 670 feet, notwithstanding the difficulties which had to be encountered on the resumption of the works, which have been already alluded to in a former part of this Report. As the tunnel approaches the opposite shore, the difficulties of the undertaking will decrease. The thickening of the crust of earth, or the bed of the river over the head of the miners, will render the more rapid advance of the shield perfectly practicable; and as the works will then be carried on under shallower water, they will be less influenced by the tides.

"In a Report made on the 24th of August to the Directors, Mr. Brunel says, ' Contrasting our present state, however, with almost the whole course of June last, it will be seen that we have gained considerably in every respect. On many occasions in June we were obliged to block up and timber the top boxes, and even to suspend our proceedings until we could approach, as it were, the top polings and probe the ground; but since and from the auxiliary means which I adopted on the 2d of July, and made an application of on that day, not one single instance is recorded of the boxes being blocked up, or of ground breaking in; on the contrary, the ground which could not be worked before, and wherein a pricker entered seven feet ahead, was worked with perfect security. We may anticipate that we shall gradually improve in progress.' The auxiliary mears alluded to in the foregoing Report, and which can only be generally described, consist of a system of pinning and isolating a portion of ground, which is then removed without disturbing the contiguous portion from which it is taken, and which has enabled the work of excavation to proceed under the most formidable circumstances. This .system, combined with a mode now adopted of at onee conveying away the land-springs and directing their course to the reservoirs, instead of attempting to stop their influx, has enabled the miners to proceed where difficulties have appeared at first almost insuperable.

"In Mr. Brunel the Directors continue their unabated confidence, and, in conclusion, whilst they remind the Proprietors that the work is one not yet free from both uncertainty and danger, they still desire to reiterate their opinion, that at no very distant period this great undertaking will, inspite of opposing difficulties, be completed, and a communication made between the shores of one of the deepest parts of the river, where within a small space the trade and navigation of London may almost be said to be concentrated: and that, in all probability, this communication will be made at less than halfthe expense of any communication for similar purposes within the range of the metropolis.

The dark

Our front page engraving illustrates the progress of the works. part of the tunnel is that which is finished. A, the position of the shield on the 7th of September, 1836. The light part, with dotted lines, shows the portion remaining to be done; B B are the low water-marks; C, the Rotherhithe shaft, for the entrance of foot-passengers to the tunnel; the dotted circle shows the more gradually descending roadway for carriages and waggons; D, St. Mary's Church. The part of the tunnel from low water-mark to the shaft on the Wapping side of the river (about 350 feet,) is not shown in the engraving.

THE NEWTONIAN PHILOSOPHY.

Sir, Indisposition has prevented me from sooner fulfilling the promise I made at the conclusion of my last letter.

Mr. Mackintosh objects to Newton's first law of motion, namely, "Every body continues at rest, or in uniform rectilineal motion, unless affected by some mechanical force."

Mr. Mackintosh is not the first who has objected to this law; hundreds of others have done the same, and thousands of pages have been written on the subject —from the days of Toland (one of Newton's bitterest opponents) to the present time. It has been urged, that if we grant the truth of the Copernican and Newtonian description of the planetary mo. tion, then we admit there is no such thing as rest, or uniform rectilineal motion. Nor has Newton himself any where asserted, that there really exists in nature such a thing as absolute rest, or a continual and uniform rectilineal motion.

Let it be remembered, that he has introduced a limitation in the above law, "unless affected by some mechanical force." The nature of such forces he has duly considered in his immortal

Principles of Natural Philosophy." He migh', perhaps, have been induced to assert the truth of this law, or axiom, or principle, by knowing that the planets have continued for ages, or as far as observations can be traced, without the smallest perceptible diminution of their motions; and if at any point in their orbits the forces that regulate their motions were supposed to be decomposed, that representing the centrifugal force would produce uniform rectilineal motion. But to do away with the idea of uniform rectilineal motion, would be a Source leading to continual blunders.

Professor Robinson, after enumerating and answering the objections that have been urged by a certain class of philosophers against the soundness of Newton's first law, thus concludes:

"All these differences of opinion may be completely settled by adhering to the principle, that every change is an effect.' It is a matter of fact that the human mind always considers it as such. Therefore, the law is strictly deduced from our ideas of motion and its causes; for even if it were essential to matter gradually to diminish its motion, and at last come to rest, this would not invalidate the law, because our understanding would consider this diminution as the indication of an essential, or, at least, a universal property of matter. * * * We should ascribe it to a natural retarding force, in the same way as we give this name to the weight of an arrow discharged straight up. wards. The nature of existing matter would be considered as the cause, and we should "estimate the law of its action as we have done in the case of gravity; and, as in that case, we should still suppose that were it not for this particular property, the material atom would continue its motion for ever undiminished," &c.

But let Mr. Mackintosh point out any proposition in the Principia depending on this law, and show (if he can) that it is inconsistent with facts deduced from astronomical observations.

Mr. Mackintosh accuses me of attack. ing the electrical theory with more asperity than appears to him to be needful. He may think so, but I judge otherwise Indeed, I would have acted exactly in the same way had Mr. Mackintosh been my own father, or brother, or son. I

have paid no small degree of attention to the Newtonian system; and I am free to confess, that the more I study it, the more I become satisfied of its truth. And as I find so many parts of the electrical theory opposed to that of universal gravitation, I think that, as an old correspondent of the Mechanics' Magazine, I would have neglected my duty had I allowed the subject to pass unnoticed; nor had Mr. Mackintosh any right to suppose that such would have been the case.

Mr. Mackintosh's method of accounting for the diurnal motion of the earth by means of galvanic circles and elec trical currents, &c. puts one much in mind of the whirlpools and vortices of Cleanthes and Descartes, and the celestial machinery of Eudoxes and Callippus. These philosophers placed the whole of their celestial mechanism in the heavens, where they had some chance of being seen. Mr. Mackintosh, with more cir cumspection, has entombed his under the surface of the revolving planet. Now, if we could force ourselves to believe in Mr. Mackintosh's theory, we must admit that the Supreme Architect himself is unacquainted with eternal or perpetual motion, for notwithstanding all the care he has taken to preserve the rotary and revolving motions as long as possible, still both must come to an end, and the "earth cease to revolve upon her axis." Mr. Mackintosh, in fact, tells us, that the rotary motion of the moon has already ceased! (No. 645, p. 233, 234.) It is strange (if true) that none of our astronomers have thought proper to give us any information of this astounding fact; or has Mr. Mackintosh merely made this assertion for the purpose of trying how far he could play upon the credulity of some of his readers (friend Ursa for one)? Or it may be (for I would not wish to deal harshly with him), that he had not duly considered the subject when he made this strange assertion. But be that as it may, let any one contrast this fanci ful part of his (Mr. Mackintosh's) theory with that given by Newton, and let him say which is most probable. Newton requires no complex machinery ins dé. monstrating the rotary and revolving motions; all that he requires is the figure of the planet, and a proper application of gravity, and all this is fully borne out by testing his theory with ancient and modern observations. Thus, for instance, the length of the day has

4

neither increased nor diminished by the smallest fraction of a second since Hipparchus (the father of practical astronomy) observed eclipses nearly 3000 years ago. I have still other remarks to make on the electrical theory, but these I must postpone for another communication.

I am, Sir, yours, &c.

KINCLAVEN.

MANIFOLD WRITERS.

Sir,-In answer to the inquiry of Litera," in your 690th Number, I beg to suggest the following method of procuring several copies of a letter with expedition and secrecy :

T

First write the letter with a pen on a sheet of paper (even as I am now doing), but instead of ink, employ the greasy or soapy substance well known to those who dabble in lithography, wetted with water, and which looks like a stick of Indian ink folded up in a thin sheet of lead. Then lay the letter fresh written on the face of a lithographic stone, and submit it to high-pressure for a short time; and the characters will be vividly transferred. (If the letter were held for a moment over steam to damp it, the better success of the transfer would be promoted.) Lastly, wet the stone, and print forthwith All this might be accomplished by one person "in secret," in as little

time as it has taken me to write this letter.

Yours obediently,

F. O. H. SIDMOUTH ENSIS.

London, Nov. 1, 1836.

MODE OF PRESERVING THE GAS OF BALLOONS CARBONIC ACID FOR BALLAST.

Sir, It is gratifying to know that an active movement is, at last, being inade for turning to some useful purpose a discovery, which has for so long a period been a matter more of idle curiosity than otherwise. The papers on that subject which have from time to time appeared in your excellent Magazine, will form an interesting feature in the history of aeronautics; and it is hoped that these will be continued, notwithstanding the chapters of improbabilities", which, on whole, have not as yet put forth any plausible objection to the purpose.

the

Considering the great expense which

attends the inflating of a balloon with coal-gas, owing to the unusual charge made by Gas Companies on such occa sions, it would be desirable that some means were devised whereby the volume of gas might be turned to better account than heretofore. At present a large quan tity is thrown away in order to cause the descent of the balloon, and the residue is as freely parted with when it has descended. Now, if two or more "ascents" could be made conveniently with the same volume of gas, and at the expense of one ascent, it is not unlikely that the so doing would be accounted an im. provement. The following method is simple-1st. Let a spherical, air-proof, silk bag be suspended from a hoop traversing the circumference of the balloon near the top, reach within a few feet from the neck, and be connected to the apparatus, afterwards described, by an airproof tube passing through the neck of the balloon; this bag to be the receptacle for carbonic acid gas, to be generated when the machine is required to descend. 2d. Let a small cask, 12 or 14 inches wide, be fastened beneath the car; this cask to be equally divided by a cross partition, having an aperture in the centre provided with a leaden plug, fitting closely, and raised by a wire passing through the tap; each division to have an opening for introducing substances, and the lower one an additional orifice, into which is inserted the conducting tube to the silk bag. Such an apparatus would not be obstructive, nor its weight considerable; the cask, suitably decorated, might be fixed under the car, and the tube be placed along one of the cords suspending the car.

Now, supposing that a balloon has gained a high elevation, it is necessary, in order to cause its descent, that the ascending power be overcome. To attain this end by means of the apparatus above described, it is necessary while inflating the balloon that a space be left as allowance for the distension of the balJast-bag. Now, let the stopper in the cask be raised, instantly the dilute acid will act upon the chalk, and the dense gas discharged thereby will rush with rapidity along the tube and expand the bag; the latter, by its weight, will in a short time produce the desired effect; the supply from the cask may easily be regulated and checked when necessary

ON THE FIRST EXCITEMENT AND GERMINATION OF PLANTS; WITH REMARKS ON THE FRANKLINEAN THEORY, AND THAT OF MR. MACKINTOSH.

Sir, We have endeavoured to trace a relation between the structure and functions of plants, and the properties of the surrounding elements, favouring the conelusion that electricity is the grand agent by which the several processes of vegetation are carried forward. Air, water, and solar light, have respectively been viewed as conveying electric influence to the vegetable kingdom. The predominant influence of each of these elements appears to take place in the order just mentioned; and the dry winds of March, the copious rains of April, and bright sunshine of May, appear to exhibit this succession in a general view, while the mingled and varying states of the weather show the almost continual necessity of their mingled operation in different degrees. It may here be observed by the way, that whereas the vital principle in animals is maintained by means of a portion of the atmosphere which is uniformly supplied at all seasons, and is administered to all the more perfect kinds in the exact proportion which is requisite to preserve the uniformity of their heat and vitality; that of vegetables, depending on the vicissitudes of the seasons, and even on the variations of the weather, is subject to the like vicissitudes and variations. To me it appears, that in reality they both depend upon the same subtile fluid as emanating from the sun; out whereas, plants derive it in an uncombined state from the floating winds, the condensing vapours, and the direct rays of the sun; animals imbibe it by means of the peculiar organisation of the lungs in those more copious and uniform supplies which their more elevated nature requires, by a chemical decomposition of oxygen in those organs. But

this important branch of inquiry cannot be pursued in this place. I now wish to offer a few remarks on the progress of vegetation under the influence of the several elements.

1st. The electric influence of the air in producing the first excitement and spring of vegetation, appears to depend much on the partial absence of its influences under the forms of condensing vapour, and of solar light; as these, by employing the electric fluid in the processes of growth and maturation, would direct large quantities of it from that which is all-essential in the first instance. Hence, our March commences with a total destitution of leaves in all the more foliagenous species of trees, while the annuals among herbs have disappeared. The only vegetative remains of these respective kinds are contained in the buds protruding from the trees, and the seeds which lie concealed in the soil. Thus a large proportion of those rays, which, as the season advances, are employed in the two subsequent processes of vegetation, are reserved to impart electricity to the air, as the instrument of producing the first excitement in the yet closed germs. As a farther preparation,-during the winter now at its termination, the vapours exhaled into the atmosphere in the preceding summer are gradually condensed, and conveyed into the earth in the forms of rain, snow, and hail, by which means that extraordinary dryness, which distinguishes the early spring, and is remarked by agriculturists for its salutary effects, is in part produced; and in part, probably, by the rarifying influence of the increasing rays, causing the lower strata of our climate to ascend and give place to the denser and yet drier air rushing in from regions into which fewer vapours had been exhaled, and from which they had been more completely removed by a more condensing tempera

ture.

These winds are, moreover, of use in removing all particles of moisture, together with other impurities from the exterior of plants, and from the surface of the soil; so that nothing may be left to be acted upon by the electric influence, but the buds, seeds, and emerging shoots. When the winds have sufficiently per formed their office of desiccation, that of vegetative excitement and germination seems speedily to commence. The glancing rays of the early season of the year