ON THE PROGRESS OF VEGETATION UNDER THE INFLUENCE OF VAPOURS. Sir, I am not aware that writers on vegetable physiology have directed their attention to the respective effects produced by the several elements upon the system of vegetation ; and yet it is eviden that since their properties differ so essen. tially, their modes of operation with its results must also differ materially. When we contemplate the commencement and progress of a plant from its seed, or of a new shoot from an unopened bud to a full-grown branch, we observe two marked changes which it undergoes before its arrival at maturity. To instance, in the most common and useful of grains, how different is the shooting blade from the seed whence it issued, and the formed ear from either of its preceding states; the opening leaf which issues from the bud, and the full-grown branch, with its expanded leaves and fruits, proceeding from its numerous and extended ramifications, in like manner, differ as essentially from their source and from each other. Now each of these states or stages of vegetation appears to be peculiarly adapted to a corresponding element, while it is in some degree fitted to be acted upon by either or all of them. If the bud is exactly fitted by its form, situation, and rigid texture, to receive an electrical excitement from the winds; the opening germ with its shooting leaves seems no less peculiarly suited to the action of vapours. In like manner, the full spread leaf is as manifestly adapted to the refining action of the solar beams upon its liquid contents. We shall now direct our attention to the second of these processes, or the mutual action of the opening leaf and the condensing vapour upon each other. No sooner has germination commenced than an increased supply, both of nutrition and of the principle of vitality, is required. If a dry atmosphere was requisite to the former process, one charged with vapours appears now to be as essentially requisite. The long acute points, the sharp and serrated edges, the extended surface, abounding in capillary filaments of the shooting leaf, are exactly adapted for acting electrically upon the vapours as they approach in a gradually condensing state. Its lithe movements, yielding to every breeze, enables it as it were to explore the atmosphere in search By of every vapour within its vicinity, this means it co-operates with the con portion of the subtile fluid which holds densing agency of cold by imbibing a water in the vaporous state, and causing it to settle upon its surface in the liquid form, for the reception of which its numerous pores are prepared. It was remarked, p. 540 of your last volume, that" in uncultivated countries the wea ther is mostly in the extremes ;" that rain: when it comes takes the form of an overwhelming flood, and is quickly fol lowed by a burning heat which destroys the coarse and scanty vegetation which the rain has fostered, &c. These extremes are probably averted in part by this action of the leaves upon vapours where vegetation is sufficiently abundant. In its absence a low temperature is, the sole cause of the conversion of vapours to the liquid state, which must take place suddenly when the cold has reached a certain degree, and their whole contents being discharged on the soil, must fall in torrents. Their caloric of vapour being dif fused wholly in the atmosphere, must cause a sudden great increase of heat and rarefaction, in proportion as it enters into combination with the particles of air; and, in proportion, as it remains uncom bined, must float in an electrical state, tending to produce convulsions. When, on the other hand, a due supply of luxu riant plants occupy the earth's surface, and extend their foliage through the atmosphere, their attractive influence seizes the vapours at a much higher tem perature, imbibes a large portion of their subtile fluid in the form of electricity into their substance, and causes a corre sponding portion of moisture to settle on their surface. Thus less of the one is left to combine with the air, or float elec trically in the atmosphere, and less of the other to descend upon the soil; and the absorption by plants proceeding with increasing degrees as the condensation increases, the whole process must proceed in a gradual and gentle manner till the vapours are exhausted; and those great and sudden changes in the weather attendant on a barren, uncultivated waste, in a great degree obviated. To what general causes is the nearer approaches of the temperature of our winters and summers toward a common medium than in less cultivated countries, or where the cultivation has been only partially extended, but to the exhalation of plants while in their vigour, and abounding in active foliage; and the conversion of the exhalations into the fluid and solid states during the comparative quiescence of vegetation, when their caloric is discharged into the atmosphere ? For though there are copious showers of rain in some of the hottest months, par ticularly in July, large portions of the caloric of vapour being at that active season absorbed by the leaves, a far less portion of it is suffered to pervade the atmosphere than at the opposite season, when in consequence of the general absence, or almost torpid state of vegetation, it is let loose by the converging vapours in much larger quantities. The powerful electrical attraction of the leaves for the fluid, which holds water in the state of vapour, is so clearly shown by the following experiment of Mr. Williams, that I am here induced to transcribe his account of it. "To the cup of a gold-leaf electroscope, I affixed a horizontal support of a candle; on the floor immediately under it was an earthen vessel containing hot water; the candle being lighted, hot embers were dropped into the water, which raising a cloud of vapour that passed through the candle, the electricity was collected by it, and transmitted to the electroscope, when the gold-leaf opened suddenly and struck the sides positively." Thus the presence of electric matter in vapour was demonstrated. "Some branches of trees with their foliage were now placed between the vessel on the floor and the candle; the experiment being repeated, the vapour passed through the interstices of the boughs, but the electroscope opened only half an inch; more boughs were now added, and the experiment was again repeated; a great part of the vapour still made its way through the interstices of the leaves and branches, but deprived of so large a portion of its electricity, that the gold-leaf did not diverge in the smallest degree." This sufficiently ma nifests the power of vegetation in withdrawing electric matter from vapours, and thus causing them to lose their vaporific property; but, as in this case, its action was counteracted by the heat produced by the fire and candle, instead of assisted by a low temperature, as in nature, a great part of the vapour ? escaped, and there appears every reason to conclude, that a corresponding portion of electric matter must have escaped with it. That when thus aided by the agency of cold, the effect is much greater, ap pears from the following observations of the same rural electrician. On the 15th and 16th September, 1805, respectively, there was a very dense fog. On the morning of the 15th it was attended with a perfect calm, the trees and hedges being loaded with dew, but no precipitation of the fog, and the electricity strongly positive; at 8 A.M. it began to clear away; at 10 A.M. the sun shone bright and the day was tolerably fair. On the following morning the fog was equally dense; but about 7 A.M. a gentle wind arose from the south, which, bringing new particles of vapour within the conducting influence of trees and hedges, occasioned a copious fall of vapours from the leave and small branches, but no general precipitation occurred." The conversion of the vapours to the liquid state was evidently much greater than in the case of the evaporation by heat arti ficially applied; the positive electricity, or electric matter released by the condensation, strong in proportion; but as it was at a temperature too high to admit of a general precipitation of vapour, the whole effect was still less than it would have been at a lower temperature. The influence "a gentle breeze," in aiding the operation by bringing successive portions of vapour within the conducting virtue of trees and hedges, finely illustrates its utility in promoting the general effect. If our former observations be founded in fact; if the life and vigour of plants depends much on the presence of a con siderable supply of carbonic acid to the roots; and their production of oxygen gas to the atmosphere, on a direct administration of the acid to the leaves through the medium either of air or water, it appears highly probable that this gas is conveyed to them by the process which we are considering. It has been remarked, that carbonic acid is absorbed by the leaves from water in the absence of light; a preparation being thus going forward for its future action upon them. Here, then, an interesting question arises, how far the va pours are instrumental in imparting this important element of nutrition and growth to plants? Its existence in the atmospere, in greatest abundance toward the end of the spring season and the beginning of the summer, according to the experiments of Mr. Weekes, is an interesting fact, as large portions of it must previously have been imbibed by the progressing vegetation. But its presence at this season, in such considerable quantities, seems a necessary preparation to the action of the solar beams in maintaining the verdure of the expanded leaf by extracting its oxygen. It appears probable, that during the winter months stores of carbonic acid must be imparted from the lungs of animals to the waters, either in their aerial or their liquid state, while vegetation remains comparatively dormant. Sir, I now proceed to describe the annealing process alluded to at the close of my last letter. This would be most conveniently done by means of a separate furnace, of the same construction as that used for melting the metal, but of rather larger dimensions. This is to be gradually raised to a pretty strong heat, and a piece of cast-iron of the form of the annexed figure, and about one inch thick, with holes at a, for the purpose of suspension by means of chains or iron rods, is to be heaped with dry sand, and lowered into the furnace until it has at.. tained a pretty florid red. The metal and block, on being taken out of the sand, and detached from the channel, is to be speedily and carefully removed to the iron plate, disposing the sand so that it shall afford an easy bed for the metal, and secure it from warping. The whole is to be now thickly covered with red-hot sand and re-lowered into the furnace, taking care to support the plate by means of a tile placed near the bottom of the furnace, as it would not probably hear suspension by the chains at the great heat to which it is to be raised. The expended coke from the other furnace may be thrown in afterwards, as well as a little fresh if necessary, to raise the metal to a bright red. At this point the draft of the furnace must be completely annihilated by closing and even luting up the ash-pit, which will prevent all danger of the metal re-melting. It will be convenient if the chimney and the top of the furnace can also be so closed as effectually to exclude the air. In this state the metal must be left until it be comes entirely cold, which, if the process has been well-conducted, will not be in less than from eighteen to twenty-four hours. The great object I have laboured to attain in annealing has been to raise the metal as nearly to the melting point as possible without actually attaining it, aud to cool it very gradually. One metal, indeed, which was unintentionally. raised so high as to begin to melt at one of its edges, turned out to be remarkably fine and brilliant. After the metal is removed from the furnace, the first thing to be done is to break off the git by which the block is attached, which must be attempted with great care with a sharp Lancashire file. Endeavour to break it close to the edge of the mirror, by filing gently all round that part of the git in contact with it, and be careful to touch the face side first, as the first scratch will generally determine the place where it breaks. Both the metal and block should be supported, that the git may not be broken by the weight of either before the line of fracture is well marked out by the file; when this is done, turn the metal face upwards, and leave the block unsupported; continue the careful use of the file for a very short time, and the block will usually drop off without any blow being required. I have thus described as briefly as I can, to be explicit, the most approved method I have employed in casting specula. I have reason to believe that it differs in some respects from that pursued by some of the most eminent London artists; yet, independently of my own conviction, I have had the testimony of some competent judges, amongst others the late Messrs. Charles and William Tulley, to the remarkable excellence of the metals I have made. Perhaps the most valuable property in a metal, next to that of being capable of fine polish in the first instance, is that of retaining that polish for a long period unimpaired, even under atmospherical circumstances not the most favourable. This severe test will be well borne by metals cast according to the directions above laid down, as I have been used to leave my metals constantly in their tubes undefended by any thing more than caps fitted to the ends of the tubes; and, moreover, have left them throughout the dampest seasons in outbuildings for years without their contracting any tarnish whatever, or indeed any dulness of reflection which could be detected in vision with the telescopes. Nor have I ever had to re-polish a mirror solely on account of tarnish contracted. It is much to be regretted that the composition of the metals of the late Sir William Herschel, exquisite in figure as they must have been, was very prone to tarnish, so much so as to render them sometimes, even at an early period, unfit for use. Even Sir John Herschel, now at the Cape, in a climate of which he almost speaks in raptures, states that he is obliged to have a change of metals for his 20-feet reflector, and frequently to repolish as their surfaces grow dull. In conclusion, it may be permitted me to mention what escaped me in its proper place that frequent re-melting of speculum metal is decidedly injurious to it; and, therefore, all possible care should be taken to render the first casting successful. It may, however, be re-melted once or twice, adding an equal quantity of new, without apparent injury; but it generally requires a small extra proportion of tin to make the fracture flaky and brilliant. Your most obedient servant, 18, Norton-street, Liverpool, A BOLD STROKE FOR A RAILWAY. Nothing daunted by their Parliamentary defeat of last year, the projectors of the rival lines of railway to Brighton are already in the field, and determined on another campaign. It is a pity they cannot agree to unite their forces, and thus save the expenditure of useless thousands, especially as they are now threatened with a new and formidable rival, in the person of Mr. Alexander Gordon, whilome editor of the Journal of Elemental Locomotion, and engineer in prospect to the "London and Holyhead Steam-coach and Road Company." This gentleman has given notice in the Gazette of the intention to apply for an Act for the "improvement," in whole or in part, of the road from Brighton to London, by applying a new surface, for converting the same into a hard and solid road,-just the same thing, in fact, as was to have been done on the Holyhead Line, to make it fit for the running of steamcarriages; but this is not all,-Mr. Gordon slily drags in such provisions as will enable him, if expedient, to convert the road into a regular railway. Thus he continues," and for making a tramway or ways, stoneway or ways, plateroad or roads of iron, stone, or other materials, for the passing of locomotive steamcarriages, &c. thereon;" all due powers are to be given to collect tolls and "to apportion the same between the present trustees and the persons authorised to improve the road," i. e. Mr. Gordon and his company! Messrs. Stephenson, Cundy, Rennie, and Co. had better look to it forthwith, lest some fine morning in the coming session they find not only that their own bills are thrown out, but that Mr. Gordon, while apparently asking only for powers to improve a turnpike-road, has in reality obtained the Parliamentary sanction for a new line of railway. The road Mr. G. proposes to take under his special protection is that through Croydon, Ryegate, Crawley, and Cuckfield: he starts from the Elephant and Castle. MACKINTOSH'S ELECTRICAL THEORY REPLY TO NAUTILUS. Sir,-Upon reading the observations of your correspondent Nautilus, contained in 697 of the Mechanics' Magazine, it at first appeared to me that no answer was required to his animadversions. However, upon second thoughts, I am of opinion that it may be perhaps as well to say a few words with a view to the removal of any misunderstanding which may exist in his mind, or in the minds of others of your readers. Nautilus, in the article alluded to, is fighting a shadow. He might very well have spared his examples of the merry-go-round, the bottle of crusted port, and the small globe, in his endea vours to prove what no one denies, that all the particles of a revolving body do each of them revolve upon its own ima ginary axis. I was not ignorant of this when I made the assertion that the moon does not revolve upon her axis, nor do I see any necessity to withdraw or qualify that assertion from what has been advanced by Nautilus. Kinclaven also objected to this assertion, but the parallel case of the wheels and leaden balls at once enabled him to perceive that it had not been made unadvisedly. I have no intention of entering into any controversy. with Nautilus upon the point-I readily grant the correctness of his views with respect to the imaginary axis. His remarks upon the small machine bearing my name, and which, at the time it was first constructed, between thirteen and fourteen years ago, was expected to turn out a perpetuum mobile, require an answer even less than the former. It has been laying by me for upwards of thir teen years, and had I entertained all the father's fondness for the bantling, it would not have been suffered to lay so long neglected. I am fully satisfied that no perpetual motion will ever be effected, either with that machine or any other system of mechanical combinations that may be put together; when I sent it for publication in the Mechanics' Magazine, I withheld an explanation of the cause of its failing to give a perpetual motion, under the impression that the ingenuity of some of its readers might be exercised in an attempt to discover it. The attempt of Nautilus is the first, and is a complete failure. I know well that the wheel will not, and I also know the reason why it will not go, but Nautilus has not yet made that discovery. In all that relates to declinations, right ascensions, latitude, and longitude, Nautilus appears to be in his proper element; but I am of opinion that he has made It The rapid increase in the use of Indiarubber, or caoutchouc, as a material for the manufacture of various articles, has led to a speculation, having for its object the introduction of Mr. Sievier's patents to the public, under the title of the "London Caoutchouc Company." has apparently met with a favourable reception, as the shares have been quoted in the market at a premium. To enable shareholders and others interested in the affair to form a just opinion of the utility of the inventions, the patent right of which, it appears, the Company are to purchase at a considerable expense, we now publish abstracts of the specifica tions of Mr. Sievier's three patents. The first patent, dated 1st December, 1831, is for "certain improvements in the making or manufacturing of cables, ropes, whale-fishing, and other lines; lathe and rigging bands; bags and purses; parts of which said improved articles are applicable to other useful purposes.' This invention consists in the employment of filaments or threads, India-rubber, to manufacturing elastic cables, ropes, whale-fishing, and other lines, lathe and rigger bands, bags and purses; the threads of India-rubber being previously platted over or covered with hemp, flax, silk, wool, cotton, catgut, Indian grass, strips of leather, or other fit materials. The filaments or threads of caoutchouc are prepared by cutting them into long strips, which are afterwards stretched to their utmost tension, and wound upon drums, reels, or bobbins, ready to be platted over or covered by, or interwoven with, the various materials before-mentioned. This may be done by the machinery, generally used for making sash lines, braiding, platting, or stay-lace machines, or any other machinery of the like description. The threads being thus prepared by platting over, or intermixing them with any of the above-mentioned materials, and collapsing in their length |