On the Old Road Volume Ii Part 17

271. "TWISTED STRATA.--The contortions of the limestone at the fall of the Nant d'Arpenaz, on the road from Geneva to Chamonix, are somewhat remarkable. The rock is a hard dark brown limestone, forming part of a range of secondary cliffs, which rise from 500 feet to 1000 feet above the defile which they border. The base itself is about 800 feet high. The strata bend very regularly except at _e_ and _f_,[28]

where they appear to have been fractured.

_To what Properties in Nature is it owing that the Stones in Buildings, formed originally of the frailest Materials, gradually become indurated by Exposure to the Atmosphere and by Age, and stand the Wear and Tear of Time and Weather every bit as well, in some instances much better, than the hardest and most compact Limestones and Granite?_[29]

272. In addition to the fact mentioned by Mr. Hunter[30] relative to the induration of soft sandstone, I would adduce an excellent example of the same effect in the cathedral of Basle, in Switzerland. The cathedral is wholly built of a soft coa.r.s.e-grained sandstone, of so deep a red as to resemble long-burned brick. The numerous and delicate ornaments and fine tracery on the exterior are in a state of excellent preservation, and present none of the moldering appearance so common in old cathedrals that are built of stone which, when quarried, was much harder than this sandstone. The pavement in the interior is composed of the same material; and, as almost every slab is a tomb, it is charged with the arms, names, and often statues in low relief, of those who lie below, delicately sculptured in the soft material. Yet, though these sculptures have been worn for ages by the feet of mult.i.tudes, they are very little injured; they still stand out in bold and distinct relief: not an illegible letter, not an untraceable ornament is to be found; and it is said, and I believe with truth, that they have now grown so hard as not to be in the least degree farther worn by the continual tread of thousands; and that the longer the stone is exposed to the air, the harder it becomes. The cathedral was built in 1019.

273. The causes of the different effects of air on stone must be numerous, and the investigation of them excessively difficult. With regard, first, to rocks _en ma.s.se_, if their structure be crystalline, or their composition argillaceous, the effect of the air will, I think, ordinarily, be found injurious. Thus, in granite, which has a kind of parallelogrammatic cleavage, water introduces itself into the fissures, and the result, in a sharp frost, will be a disintegration of the rocks _en ma.s.se_; and, if the felspar be predominant in the composition of the granite, it will be subject to a rapid decomposition. The morvine of some of the Chamouni and Allee Blanche glaciers is composed of a white granite, being chiefly composed of quartz and felspar, with a little chlorite. The sand and gravel at the edge of these glaciers appears far more the result of decomposition than attrition. All finely foliated rocks, slates, etc., are liable to injury from frost or wet weather. The road of the Simplon, on the Italian side, is in some parts dangerous in, or after, wet weather, on account of the rocks of slate continually falling from the overhanging mountains above; this, however, is mere disintegration, not decomposition. Not so with the breccias of Central Switzerland. The rock of Righi is composed of pebbles of different kinds, joined by a red argillaceous gluten. When this rock has not been exposed to the air, it is very hard: you may almost as easily break the pebbles as detach them from their matrix; but, when exposed for a few years to wind and weather, the matrix becomes soft, and the pebbles may be easily detached. I was struck with the difference between this rock and a breccia at Epinal, in France, where the matrix was a red sandstone, like that of the cathedral at Basle. Here, though the rock had every appearance of having been long exposed to the air, it was as hard as iron; and it was utterly impossible to detach any of the pebbles from the bed: it was difficult even to break the rock at all. I cannot positively state that the gluten in these sandstones is calcareous, but I suppose it to have been so. Compact calcareous rock, as far as I remember, appears to be subject to no injury from the weather. Many churches in Italy, and almost the whole cities of Venice and Genoa, are built of very fine marble; and the perfection of the delicate carvings, however aged, is most remarkable. I remember a church, near Pavia, coated with the finest and most expensive marbles; a range of beautifully sculptured medallions running round its base, though old, were as distinct and fine in their execution as if they had just come out of the sculptor's studio. If, therefore, the gluten of the sandstone be either calcareous or siliceous, it will naturally produce the effect above alluded to, though it is certainly singular that the stone should be soft when first quarried. Sandstone is a rock in which you seldom see many cracks or fissures in the strata: they are generally continuous and solid. Now, there may be a certain degree of density in the ma.s.s, which could not be increased without producing, as in granite, fissures running through it: the particles may be supposed to be held in a certain degree of tension, and there may be a tendency to what the French call _a.s.saiss.e.m.e.nt_ (I do not know the English term), which is, nevertheless, resisted by the stone _en ma.s.se_; and a quant.i.ty of water may likewise be held, not in a state of chemical combination, but in one of close mixture with the rock. On being broken or quarried, the _a.s.saiss.e.m.e.nt_ may take place, the particles of stone may draw closer together, the attraction become stronger; and, on the exposure to the air, the water, however intimately combined, will, in a process of years, be driven off, occasioning the consolidation of the calcareous, and the near approach of the siliceous, particles, and a consequent gradual induration of the whole body of the stone. I offer this supposition with all diffidence; there may be many other causes, which cannot be developed until proper experiments have been made. It would be interesting to ascertain the relative hardness of different specimens of sandstone, taken from different depths in a bed, the surface of which was exposed to the air, as of specimens exposed to the air for different lengths of time.

J. R.

HERNE HILL, _July 25, 1836._

FOOTNOTES:

[Footnote 27: London's _Magazine of Natural History_, Vol. vii., pp.

644-5. The note was ill.u.s.trated by engravings from two sketches by the author of the Aiguille de Servoz and of the Aiguille Dru, and by a diagram explanatory of its last sentence but one.--ED.]

[Footnote 28: "A small neat copy of a sketch carefully taken on the spot," which, according to the editor of the magazine, accompanied this communication, was not, however, published. See the magazine.--ED.]

[Footnote 29: Loudon's _Magazine of Natural History_, Vol. ix., No. 65, pp. 488-90.--ED.]

[Footnote 30: The question here discussed was originally asked in the magazine (Vol. ix., pp. 379-80) by Mr. W. Perceval Hunter with reference to the condition of Bodiam Castle, in Suss.e.x.--ED.]

OBSERVATIONS ON THE CAUSES WHICH OCCASION THE VARIATION OF TEMPERATURE BETWEEN SPRING AND RIVER WATER.--BY J. R.[31]

274. The difference in temperature between river and spring water, which gives rise to the query of your correspondent Indigena (p. 491),[32] may be the result of many causes, the princ.i.p.al of which is, however, without doubt, the interior heat of the earth. It is a well known fact, that this heat increases in a considerable ratio as we descend, making a difference of several degrees between the temperature of the earth at its surface and at depths of 500 or 600 feet; raising, of course, the temperature of all springs which have their source at even moderate depths, and entirely securing them from the effects of frost, which, it is well known, cannot penetrate the earth to a greater depth than 3 or 4 ft.

275. Many instances might be given of the strong effect of this interior heat. The glaciers of the Alps, for instance, frequently cover an extent of three or four square leagues, with a ma.s.s of ice 400, 500, or even 600 feet deep, thus entirely preventing the access of exterior heat to the soil; yet the radiation of heat from the ground itself is so powerful as to dissolve the ice very rapidly, and to occasion streams of no inconsiderable size beneath the ice, whose temperature, in summer, is, I believe, as far as can be ascertained, not many degrees below that of streams exposed to the air; and the radiation of heat from the water of these streams forms vaults under the ice, which are frequently 40 ft.

or 50 ft. above the water; and which are formed, as a glance will show, not by the force of the stream, which would only tear itself a broken cave sufficient for its pa.s.sage, but by the heat which radiates from it, and gives the arch its immense height, and beautifully regular form.

These streams continue to flow in winter as well as in summer, although in less quant.i.ty; and it is this process which chiefly prevents the glacier from increasing in size; for the melting at the surface is, in comparison, very inconsiderable, even in summer, the wind being cold, the sun having little power, and slight frosts being frequent during the night. It is also this melting beneath the ice (subglacial, suppose we call it) which loosens the ice from the ground, and occasions, or rather permits, the perpetual downward movement, with which

"The glacier's cold and restless ma.s.s Moves onward day by day."

276. But more forcible and striking evidence is afforded by experiments made in mines of great depth. Between 60 ft. and 80 ft. down, the temperature of the earth is, I believe, the same at all times and in all places; and below this depth it gradually increases. Near Bex, in the Valais, there is a perpendicular shaft 677 ft. deep, or about 732 ft.

English, with water at the bottom, the temperature of which was ascertained by Saussure. He does not tell us whether he used Reaumur's or the centesimal thermometer; but the result of his experiment was this:--In a lateral gallery, connected with the main shaft, but deserted, and, therefore, unaffected by breath or the heat of lamps, at 321 ft. 10 in. below the surface, the temperature of the water and the air was exactly the same, 11-1/2; or, if the centesimal thermometer was used, 52-4/5 Fahr.; if Reaumur's, 57-7/8 Fahr.

277. In another gallery, 564 feet below the surface, the water and air had likewise the same temperature, 12-1/2, either 54-4/5 or 6O-1/4 Fahr. The water at the bottom, 677 feet, was 14, 57-1/2 or 63-1/4 Fahr.

The ratio in which the heat increases, therefore, increased as we descend, since a difference of 113 feet between the depth of the bottom of the shaft and the lowest gallery makes a greater difference in temperature than the difference of 243 feet between the lowest and upper gallery. This heat is the more striking when it is considered that the water is impregnated with salt; indeed, Saussure appears inclined to consider it accidental, perhaps occasioned by the combustion of pyrites, or other causes in the interior of the mountain ("Voyages dans les Alpes," tom. iv., c. 50). All experiments of this kind, indeed, are liable to error, from the frequent occurrence of warm springs, and other accidental causes of increase in temperature. The water at the bottom of deep lakes is always found several degrees colder than the atmosphere, even when the water at the surface is warmer: but that may be accounted for by the difference in the specific gravity of water at different temperatures; and, as the heat of the sun and atmosphere in summer is greater than the mean heat of the earth at moderate depths, the water at the bottom, even if it becomes of the same heat with the earth, must be colder than that at the surface, which, from its exposure to the sun, becomes frequently warmer than the air. The same causes affect the temperature of the sea; and the greater saturation of the water below with salt renders it yet more susceptible of cold. Under-currents from the poles, and the sinking of the water of low temperature, which results from the melting of the icebergs which float into warmer lat.i.tudes, contribute still farther to lower the temperature of the deep sea. If, then, the temperature of the sea at great depths is found not many degrees lower than that at the surface, it would be a striking proof of the effect produced by the heat of the earth; but I am not aware of the results of the experiments which have been made on this subject.

278. We must, then, rest satisfied with the well-ascertained fact, that the temperature of the earth, even at depths of a few feet, never descends, in temperate lat.i.tudes, to the freezing point; and that at the depth of 60 feet it is always the same, in winter much higher, in summer considerably lower, than that of the atmosphere. Spring water, then, which has its source at a considerable depth, will, when it first rises, be of this mean temperature; while, after it has flowed for some distance, it becomes of the temperature of the atmosphere, or, in summer, even warmer, owing to the action of the sun, both directly and reflected or radiated from its bottom. Besides this equable temperature in the water itself, spring or well water is usually covered; and, even if exposed, if the well is very deep, the water will not freeze, or at least very slightly; for frost does not act with its full power, except where there is a free circulation of air. In open ponds, wherever bushes hang over the water, the ice is weak. Indigena's supposition, that there are earthy particles in river water, which render it more susceptible of cold than spring water, cannot be true; for then the relative temperatures would be the same in winter and in summer, which is not the case; and, besides, there are frequently more earthy particles in mineral springs, or even common land springs, than in clear river water, provided it has not been fouled by extraneous matter; for it has a tendency to deposit the earthy particles which it holds in suspension.

279. It is evident, also, that the supposition of Mr. Carr (Vol. v., p.

395) relative to anchor frosts, that the stones at the bottom acquire a greater degree of cold, or, to speak more correctly, lose more heat, than the water, is erroneous. J. G. has given the reasons at p. 770; and the glaciers of Switzerland afford us an example. When a stone is deposited on a glacier of any considerable size, but not larger than 1 foot or 18 inches in diameter, it becomes penetrated with the heat of the sun, melts the ice below it, and sinks into the glacier. But this effect does not cease, as might be supposed, when the stone sinks beneath the water which it has formed; on the contrary, it continues to absorb heat from the rays of the sun, to keep the water above it liquid by its radiation, and to sink deeper into the body of the glacier, until it gets down beyond the reach of the sun's rays, when the water of the well which it has formed is no longer kept liquid, and the stone is buried in the ice. In summer, however, the water is kept liquid; and circular wells, formed in this manner, are of frequent occurrence on the glaciers, sometimes, in the morning, covered by a thin crust of ice.

Thus, the stones at the bottom of streams must tend to raise, rather than lower, this temperature. Is it possible that, in the agitation of a stream at its bottom, if violent, momentary and minute vacua may be formed, tending to increase the intensity of the cold?

HERNE HILL, _Sept. 2, 1836._

FOOTNOTES:

[Footnote 31: London's _Magazine of Natural History_, vol. ix., pp.

533-536.--ED.]

[Footnote 32: The query was as follows:--

_An Inquiry for the Cause of the Difference in Temperature of River Water and Spring Water, both in Summer and Winter._--In the summer time the river water is much warmer than that from a spring; during the severe frosts of winter it is colder; and when the stream is covered over with ice, the spring, that is, well or pump water is unaffected by frost. Does this difference proceed from the exposure of the surface of the river water, in summer, to the sun's direct influence, and, in winter, to that of frost; while the well water, being covered, is protected from their power? Or is there in river water, from the earthy particles it contains, a greater susceptibility of heat and cold?--_Indigena_. _April 19, 1836._--ED.]

METEOROLOGY.[33]

280. The comparison and estimation of the relative advantages of separate departments of science is a task which is always partially executed, because it is never entered upon with an unbiased mind; for, since it is only the accurate knowledge of a science which can enable us to present its beauty, or estimate its utility, the branches of knowledge with which we are most familiar will always appear the most important. The endeavor, therefore, to judge of the relative _beauty_ or _interest_ of the sciences is utterly hopeless. Let the astronomer boast of the magnificence of his speculations, the mathematician of the immutability of his facts, the chemist of the infinity of his combinations, and we will admit that they all have equal ground for their enthusiasm. But the highest standard of estimation is that of utility. The far greater proportion of mankind, the uninformed, who are unable to perceive the beauty of the sciences whose benefits they experience, are the true, the just, the only judges of their relative importance. It is they who feel what impartial men of learning know, that the ma.s.s of general knowledge is a perfect and beautiful body, among whose members there should be no schism, and whose prosperity must always be greatest when none are partially pursued, and none unduly rejected. We do not, therefore, advance any proud and unjustifiable claims to the superiority of that branch of science for the furtherance of which this society has been formed over all others; but we zealously come forward to deprecate the apathy with which it has long been regarded, to dissipate the prejudices which that apathy alone could have engendered, and to vindicate its claims to an honorable and equal position among the proud thrones of its sister sciences. We do not bring meteorology forward as a pursuit adapted for the occupation of tedious leisure, or the amus.e.m.e.nt of a careless hour. Such qualifications are no inducements to its pursuit by men of science and learning, and to these alone do we now address ourselves. Neither do we advance it on the ground of its interest or beauty, though it is a science possessing both in no ordinary degree. As to its beauty, it may be remarked that it is not calculated to harden the mind it strengthens, and bind it down to the measurement of magnitudes and estimation of quant.i.ties, destroying all higher feelings, all finer sensibilities: it is not to be learned among the gaseous exhalations of the deathful laboratory; it has no dwelling in the cold caves of the dark earth; it is not to be followed up among the charnel houses of creation. But it is a science of the pure air, and of the bright heaven; its thoughts are amidst the loveliness of creation; it leads the mind, as well as the eye, to the morning mist, and the noonday glory, and the twilight-cloud, to the purple peace of the mountain heaven, to the cloudy repose of the green valley; now expatiating in the silence of stormless ether, now on the rushing of the wings of the wind. It is indeed a knowledge which must be felt to be, in its very essence, full of the soul of the beautiful. For its interest, it is universal, unabated in every place, and in all time. He, whose kingdom is the heaven, can never meet with an uninteresting s.p.a.ce, can never exhaust the phenomena of an hour; he is in a realm of perpetual change, of eternal motion, of infinite mystery. Light and darkness, and cold and heat, are to him as friends of familiar countenance, but of infinite variety of conversation; and while the geologist yearns for the mountain, the botanist for the field, and the mathematician for the study, the meteorologist, like a spirit of a higher order than any, rejoices in the kingdoms of the air.

281. But, as we before said, it is neither for its interest, nor for its beauty, that we recommend the study of meteorology. It involves questions of the highest practical importance, and the solution of which will be productive of most substantial benefit to those cla.s.ses who can least comprehend the speculations from which these advantages are derived. Times and seasons and climates, calms and tempests, clouds and winds, whose alternations appear to the inexperienced mind the confused consequences of irregular, indefinite, and accidental causes, arrange themselves before the meteorologist in beautiful succession of undisturbed order, in direct derivation from definite causes; it is for him to trace the path of the tempest round the globe, to point out the place whence it arose, to foretell the time of its decline, to follow the hours around the earth, as she "spins beneath her pyramid of night,"

to feel the pulses of ocean, to pursue the course of its currents and its changes, to measure the power, direction, and duration of mysterious and invisible influences, and to a.s.sign constant and regular periods to the seedtime and harvest, cold and heat, summer and winter, day and night, which we know shall not cease, till the universe be no more. It may be thought we are exaggerating the effects of a science which is yet in its infancy. But it must be remembered that we are not speaking of its attained, but of its attainable power: it is the young Hercules for the fostering of whose strength the Meteorological Society has been formed.

282. There is one point, it must now be observed, in which the science of meteorology differs from all others. A Galileo, or a Newton, by the una.s.sisted workings of his solitary mind, may discover the secrets of the heavens, and form a new system of astronomy. A Davy in his lonely meditations on the crags of Cornwall, or in his solitary laboratory, might discover the most sublime mysteries of nature, and trace out the most intricate combinations of her elements. But the meteorologist is impotent if alone; his observations are useless; for they are made upon a point, while the speculations to be derived from them must be on s.p.a.ce. It is of no avail that he changes his position, ignorant of what is pa.s.sing behind him and before; he desires to estimate the movements of s.p.a.ce, and can only observe the dancing of atoms; he would calculate the currents of the atmosphere of the world, while he only knows the direction of a breeze. It is perhaps for this reason that the cause of meteorology has. .h.i.therto been so slightly supported; no progress can be made by the most gigantic efforts of a solitary intellect, and the co-operation demanded was difficult to obtain, because it was necessary that the individuals should think, observe, and act simultaneously, though separated from each other by distances on the greatness of which depended the utility of the observations.

283. The Meteorological Society, therefore, has been formed, not for a city, nor for a kingdom, but for the world. It wishes to be the central point, the moving power of a vast machine, and it feels that unless it can be this, it must be powerless; if it cannot do all, it can do nothing. It desires to have at its command, at stated periods, perfect systems of methodical and simultaneous observations,--it wishes its influence and its power to be omnipotent over the globe, so that it may be able to know, at any given instant, the state of the atmosphere at every point on its surface. Let it not be supposed that this is a chimerical imagination, the vain dream of a few philosophical enthusiasts. It is co-operation which we now come forward to request, in full confidence, that if our efforts are met with a zeal worthy of the cause, our a.s.sociates will be astonished, _individually_, by the result of their labors in a body. Let none be discouraged because they are alone, or far distant from their a.s.sociates. What was formerly weakness will now have become strength. Let the pastor of the Alps observe the variations of his mountain winds; let the voyagers send us notes of the changes on the surface of the sea; let the solitary dweller in the American prairie observe the pa.s.sages of the storms, and the variations of the climate; and each, who alone would have been powerless, will find himself a part of one mighty mind, a ray of light entering into one vast eye, a member of a mult.i.tudinous power, contributing to the knowledge, and aiding the efforts, which will be capable of solving the most deeply hidden problems of nature, penetrating into the most occult causes, and reducing to principle and order the vast mult.i.tude of beautiful and wonderful phenomena by which the wisdom and benevolence of the Supreme Deity regulates the course of the times and the seasons, robes the globe with verdure and fruitfulness, and adapts it to minister to the wants, and contribute to the felicity, of the innumerable tribes of animated existence.

OXFORD UNIVERSITY.

FOOTNOTES:

[Footnote 33: From the "Transactions of the Meteorological Society,"

Vol. i., pp. 56-9 (London, 1839). The full t.i.tle of the paper was "Remarks on the Present State of Meteorological Science." The Society was inst.i.tuted in 1823, but appears to have published no previous transactions.--ED.]

ON TREE TWIGS.[34]

284. The speaker's purpose was to exhibit the development of the common forms of branch, in dicotyledonous trees, from the fixed type of the annual shoot. Three princ.i.p.al modes of increase and growth might be distinguished in all acc.u.mulative change, namely:--