V.—MRWITHERS.Having by chance glanced over a pamphlet by an Englishman, a Mr Withers, we find there has been jousting between that gentleman and our Scottish knights, backed by their squire the Edinburgh Reviewer, in which the discomfiture of the knights has been wrought by simple hands.
Having by chance glanced over a pamphlet by an Englishman, a Mr Withers, we find there has been jousting between that gentleman and our Scottish knights, backed by their squire the Edinburgh Reviewer, in which the discomfiture of the knights has been wrought by simple hands.
It seems Sir Henry Steuart, forgetful that his own bright fame, which rivals that of the discoverers of steam-power and gas42, though of comparatively quick growth, will endure for ages; and led astray, probably, by the foolish adage, “soon ripe, soon rotten,” had stated unqualifiedly, that “fast grown timber will sooner decay, and is of opener weaker texture than slow grown of the same kind;” and on these false premises concluded, that all culture or application of manure to further the growth of timber is improper—winding up with some patriotic flourish about danger to our war navy, from Mr Withers{199}rendering the British oak of such exceedingly rapid growth as to be soft and perishable as mushrooms. Withers completely demolishes his literary and scientific adversaries, but is, withal, so very imperfectly acquainted with the subject—himself, and also his junto of experienced correspondents, that we shall attempt a few lines in elucidation.
We shall first state our facts, accompanied with explanatory remarks.
No. 1. An ash tree of about 18 inches diameter, and 65 years of age. The first 35 years, the annual growths were of middle size, and the timber weighty and tough; the following 15 years, very small, light, porous, and free; the latter 15 of middle size, and of fair quality. This tree had been growing till about 49 years of age in a grassy avenue, of dry clay soil, and close by a deep ditch. About sixteen years back, the ditch had been filled up, and the ground ploughed and manured regularly till the tree was cut down. After 35 years’ growth, the scorching roots of the ash had rendered the soil so dry, that the tree had run entirely to reproduction:Nearly all the nourishment from the ground assimilated in the leaves being expended in forming seed, no extension of the top had taken place, and{200}thence no thickening of the bole being necessary for support, no wood proper had been deposited on the trunk save the annual rings of lineal tubes to convey the sap, which constituted a brittle light wood, of very slight lateral adhesion43. After the ditch was filled up, and the surrounding ground ploughed and manured, the increased supply of moisture and nourishment had induced a considerable new extension of top (which was quite visible in fine young healthy branches rising from a stunted base), and consequent necessary thickening of stem by annual layers of proper dense wood, along with the lineal annual tubes.
No. 2. A beautiful most luxuriant growing oak, in one of the sweetest sunny spots of the sweetest valley of our Highlands. This tree, of nearly two hundred solid feet of timber, and 80 years of age, was growing upon the bare shelf of a sound mica-schist rock. From underneath this shelf, several feet down in front, a most exuberant spring welled out, and the roots spread down over{201}the rock to the mouth of the crystal spring, no doubt tracing inward the course of the limpid waters into the rocky chambers of the Naiad. We had much conjecture how this tree came to be growing on the bare shelf, and finally concluded, that the nymph of the spring, while she sat there gazing on her beauties, under the varying dimpling reflection of the living waters, her rosy feet bathed by the glassy flood, had been surprised by some rude Celt, and to effect escape from his rough embrace, had been transformed by Diana into a tree. Yet whether of natural or supernatural origin, it was by the people of the glen held of miraculous virtue, and the sickly children were brought to be dipped in the spring after being borne several times round the charm-tree. When torn from its seat, the tree, though sound, and having a level fall (we saw it fall), broke across about twenty feet up, where the stem was about eight feet in circuit;this was owing to the very soft tender nature of the wood, which, although consisting of very large annual growths, was, when sawn out, the most porous insufficient Scots oak we have ever seen. As this fact may be ascribed to the supernatural,—the heart of the nymph beginning to soften towards the Celt at the time Diana interfered, accounting well for{202}the soft texture of the heart-wood of the tree, we shall not press it as a proof on either side of the controversy. Perhaps sober reasoners may think this all phantasy, and conclude, that the tree, from deficiency of substantial earthy food, and subsisting principally onslops(being mainly nourished by drinking of the delicious well), would, like an animal under similar circumstances, be of soft flabby consistency.
The above fact is opposed to common opinion—a Highlander always choosing his oaken staff from off a rock, as being most to depend upon; yet perhaps this preference is owing to some association with the hardness of the rock itself.
No. 3. We found a sycamore plane (Acer pseudo-platanus) in the same row with other sycamores, and about the same size, so exceeding hard that it could scarcely be cut down by mattock and hatchet, whereas the others adjacent were comparatively of moderate hardness, though differing considerably in hardness from each other; the soil in this case was very equable, being of Carse clay. The peculiar hardness of this tree could only be attributable to a harder variety. Indeed, the difference of quality in timber depends chiefly on the infinite varieties existing in what is called Species, though soil and{203}climate have no doubt considerable influence, both in forming the variety, and in modifying it while growing. Of varieties, those which have the thinnest bark, under equal exposure, have the hardest wood.
No. 4. We have cut a number of large old ash trees, and found, with one or two exceptions, of what is called thunder-struck trees (which we consider only an obdurate variety), that they were invariably of very free, weak consistency, more especially the latter formed growths, but even the earlier growths had becomefrushfrom age. This timber soon went to decay after being cut down:—one piece cut out into planks, and these being laid down in the order they occupied in the log, was in the course of some weeks rendered again entire by being agglutinated by Jew’s ears (a species of fungus.) The workmen were greatly startled at the fact, thinking the log bewitched. When immediately dissevered by wedges, the wood was so much decomposed, that its fibre was tenderer than the Jew’s ears, separating in a new course in most places, in preference to the saw draught occupied by the ears. We have found very old oaks have exactly the same friable character, so much so, as render their safe felling almost impossible; yet this oak timber had not lost much in weight{204}when compared after being dried with younger oak.
No. 5. We cut a row of ash trees, about 50 years of age, in dry Carse clay, by the side of a deep ditch, and consequently of slow growth; the timber was excellent, hard, strong, and weighty, rather most so where the size was smallest. At one end, where the row approached a brook, and the soil became richer and moister, several of the trees were of good size, but rather inferior in quality of timber, excepting one (the largest, though not the nearest to the brook), which was of very hard, strong, and reedy fibre, evidently a variety differing much from the others. It is always easy to discriminate pretty accurately the quality of the wood, by examination of the saw cross section of the trunk, that is, provided the same saw be employed, and be kept equally sharp; the best timber having the glossiest, smoothest section.
No. 6. We have examined Scots fir grown in many different situations; by far the best quality, of its age, of any we know, stands upon a very adhesive Carse clay, which, from the proprietor’s neglect, is all winter and in wet weather soaking with water, and the trees not of very luxuriant growth. These, till a few years ago, stood in close order, without the stem being{205}much exposed to parching or evaporation; this exposure of the stem rendering fir timber much harder and more resinous. Every body who has touched larch must be convinced that the slow grown on poortills, especially with long naked stems in exposed situation, is very much stronger and harder than the quick grown, though often not so tough: but much depends on the variety in larch, those having the reddest matured wood being much harder than the paler coloured.
Memel fir, which is the largest growthed red pine we are acquainted with, is very strong and durable, probably next to the pitch pine of North America; yet the very large growthed Memel is generally weakest, though we frequently find a log of small growthed, mild and inferior in strength. In old buildings we have often witnessed the beautiful small growthed red wood pine wormed, when the larger growthed was sound, but we are sensible that spontaneous decomposition and consumption by insects are very different; much resin deters insects, whereas, in moist situations, as in treenails of vessels, it conduces to spontaneous decay; yet is it preservative when the timber is exposed to the weather by excluding the rain.{206}
The coniferæ differ much in the internal arrangement of their woody structure from the hard wood species, having tissue of much larger cells, and being generally destitute of the large lineal tubes, which in hard wood constitute the more porous inner part of the annual layer. When these tubes occur in the pines, they also differ in position, being in the outer part of the layer. Owing to the resin of the pines becoming fixed in the cells of the outer part of the annual layers, inspissated, we think, by the summer’s heat and drought (others say congealed by the cold), these cells are filled up, and this part of the growth rendered much denser than the inner part of the layer, being from solidity semi-transparent. We would attribute the abundance of resin in the Georgian pitch pine to the heat and long summer of that country, probably in concert with damp richness of soil, not only occasioning this deposit under these circumstances, but perhaps inducing a disposition in this species to the formation of this product44. The absence of the large tubes,{207}and the presence of oleaginous resin, render pine timber, when old and small growthed, not so brittle, nor so liable to decay, as that of deciduous trees; but it becomes very deficient in lateral adhesion. From the same cause we find the external layers of matured pine timber comparatively superior to the quality of the inner layers: in hard wood the exterior layers are generally much inferior to the inner. Boards of sap-wood of fast grown Scots fir, particularly of the outside layers are much better suited—stronger and more lasting, for boxes used as carriage packages, or for machinery or cart lining much exposed to blows and friction; than boards of the best matured red wood of Memel, Swedish, or Norway pine. This is principally owing to the fast grown alburnum possessing much greater lateral adhesion than the matured wood of old pines. To have these sap-wood boards in greatest perfection, the tree must{208}not lie in the bark after felling, and the boards must be well dried soon after being cut out. To expose the tree, peeled, either standing or felled, to the sun and dry air for some time, will considerably increase the strength of this alburnum. The wood, while in the state of sap-wood, of many kinds of timber is as strong and much tougher than the same wood after being matured, and would be equally valuable were any process discovered of rendering it equally durable; its insufficiency often arises from partial decay having occurred while in the log. The same sap-wood of oak, which, allowed to lie on the grass after being peeled in spring, will be so much decomposed in autumn that it may be kicked off with one’s heel; if cut out and dried immediately on being felled, it will be tougher than the matured, and, kept dry as cart-spokes, and defended by paint from the worm, will last and retain its toughness for an age. The tilling up, which to a certain extent occurs in maturing, is most probably deposited to fill up tubes, and may thus not greatly strengthen the mass; a hollow cylinder being stronger than a solid cylinder when extending horizontally over a considerable stretch, like a joist or beam; the mass may also become a little more fragile by maturing: besides a filling up is the result of some chemical change the{209}wood probably becoming slightly carbonized or approaching to that change which takes place when vegetables become peat.
It is rather difficult to speak of the strength of timber, as different kinds of timber, and different parts and qualities of the same kind of timber, have different kinds of strength. Some kinds are stronger as beams or joists, other kinds as boarding; while, again, some kinds are better for enduring a regular pressure, others for supporting a sudden jerk or blow, either as beams or boards. Some kinds are also comparatively stronger, moist; others when dry—and some kinds retain their qualities of strength or toughness longer than others when moist, and others longer when dry, although no rot appear.
No. 7. Purposely for experiment45, we selected three ash trees, all growing in Carse clay, but differing the most in fastness of growth of any we could discover. We cut these down on the same day; two of them proved about 36 years planted, and the third 15; this, the youngest was of fast growth, and had layers of more than double the size of one of the{210}former, and about six times that of the other. We cut a number of pieces of exactly equal length and thickness (17 inches long, and nearly an inch on the side), from each of these, choosing them of clean straight fibre, at equal distance from the ground, and from the outside of the tree, and having their growths nearly parallel to one side, of course free of heart. We proved one of each immediately on being cut out while full of sap, with their growths on edge in horizontal position, supported at each end with a weight suspended from the middle. The smallest growthed, and the largest, weighed at the time of trial nearly equal; the medium growthed one-thirtieth more. The smallest growthed supported the weight about six minutes; the medium and the largest about half that time; the smallest growthed yielded the least before breaking, and the largest yielded the most. When completely dried, the weight of the medium growthed still continued greatest, surpassing the largest one-fourteenth, and the smallest about one-thirtieth. The smallest and medium supported nearly equal weight, during equal time, and outbore the largest about one-seventh46; when placed{211}with the growths on edge, they were stronger than when placed with the growths flat.
After these rather lengthy references to facts, we must allude to a circumstance which we are astonished has not been attended to by Mr Withers, and his gentlemen correspondents connected with His Majesty’s docks,—the not taking into account the place of the tree whence the portion of wood for experimenting the strength had been taken, and also how the annual layers stood, whether horizontal or on edge, or around a centre, when the weight was applied. The experienced and accurately practical Mr Withers presents two specimens of oak, the one of faster and the other of slower growth, to Professor Barlow, of Woolwich Royal Academy, and the strength of these specimens is tested and reported upon, without once alluding to what we have mentioned above. Now, if this has not been attended to, the experiment may be considered a test of something else than of the timber. How much the strength is affected by the place of the tree, any person may satisfy himself by proving one piece of timber taken from near the root, another half way up the tree, and a third near the top: he will find that in a tall tree the comparative{212}strength will sometimes vary as much as 3, 2, 1; that is, a beam, say 2 inches square, and 4 feet long, taken from near the root, when horizontally placed, and resting only at each end, will support three times as much as a like beam in like position from near the top of the tree, although both are equally clear of knots or cross section of grain. This is particularly manifest in large fast-grown silver fir and old ash, and the difference is always greatest in old trees. He will also find that the position of the beam, in respect to the layers being circular round the heart, flat, on edge, or at an angle, has considerable influence, and, should he inquire farther, will perhaps notice, that the timber from different sides of the tree is not always alike strong; that one specimen of timber will be superior to another, both being moist, and inferior to it when both are dry, and that also, as in No. 1, the tree at the same height on the same side, will contain timber differing in strength fully one half, and not always diminishing in strength from the heart outwards, even in hard wood. We are well pleased with one gentleman of the Navy Dock-yard, who naively admits, that he is incompetent to decide on these subjects, having been altogether devoted to the mathematical, in estimating the strain and resistance timber suffers under{213}different combinations. Now we like this division of labour.
But to return to our subject. The facts stated go to prove, that the quality of timber depends much upon soil, circumstance, and more especially on variety; and that in the early period of the growth of trees, before much seeding, and when the soil is not much exhausted of the particular pabulum necessary for the kind of plant, that rather slow grown timber is superior in strength to quick grown, especially when the quickness exceeds a certain degree; when this degree is exceeded, the timber is not so weighty, and is well known not to be so durable. However, when timber is required of considerable scantling, it is only in good soils, where the tree increases moderately fast, that timber will attain sufficient size for this, at an age young enough to retain its toughness throughout, or to continue forming firm dense wood on the exterior. This is particularly so in the case of hard-wood timber, more especially when oak grows upon a moist soil, where the matured wood, of brownish-red colour, is often unsound, and where decay commences at a comparatively early period. In the pine, owing to the oleaginous undrying nature of the sap (resin), the{214}timber retains its strength to a great age; and the reedy closeness of slow growth, for most purposes, outbalances any loss from deficiency of lateral adhesion.
Moderately fast grown timber is much more requisite for naval purposes than for other uses; as, besides the greater longitudinal strength when of large dimension, it has greater adhesion laterally, is far more pliant, and therefore much better suited for the ribs of vessels, where cross cutting a portion of the fibre, from the inattention to training to proper bends, is unavoidable; and whence a disrupting shock (which is rather to be withstood than fair pressure), makes the unyielding splintering old wood fly like ice; the rift commencing its run from the cut fibre. For plank, the lateral adhesion and pliancy of young moderately fast grown timber is equally valuable, especially for those which are applied to the curvature of the bow and stern. Young timber also softens much better by steam, therefore is more convenient for planking, and for being bent for the compass timbers of large vessels. The vessel constructed of it will besides, from the general elasticity of the fibre, be more lively in the water, sail faster, and, though stronger to resist, will{215}have less strain to endure47. Mr Withers’s corresponding friends, especially those of his Majesty’s Dock-yards, with the good common sense of practical men, are well acquainted with all this, although they get a little out of element when they meddle with nature or causes. Mr Withers is himself equally out of element when he expatiates on the mighty advantage of trenching and manuring at planting, and when he talks of our Scottish holes. The Knight, too, is still more at fault in dreading any great influence on the quickness of the growth of trees from this gentleman’snew inventions,—and doubly at fault, from conjecturing our navy would suffer from being constructed of the fastest grown British timber there is any chance of our shipwrights obtaining. Since we were in our teens, we have almost every season trenched a portion of ground for planting, and have manured highly at planting48,{216}and for several years afterwards. We have found, when very adhesive subsoil was brought upward, that the trees throvewellwhile the ground continued under cultivation; but when the labour ceased, they were soon overtaken by those planted at the same time without trenching. This comparative falling off was evidently owing to the surface being rendered more adhesive by the gluey plastic subsoil being mixed upward with the original small portion of surface-mould. This new surface melted to a pulp by the winter rains, when drought set in spring, run together, became indurated, and parting into divisions, admitted the drought down to the unstirred ground by numerous deep and wide cracks, which rent the rootlets of the trees, and rendered it impossible for any plant to thrive. There are also many kinds of light subsoil, which it would be folly to bring to the surface, and where little profit would arise from deep stirring, even though the surface were retained uppermost.
In cases where the plants were very small, we have found deep trenching of no benefit, but in certain{217}soils rather hurtful, even during the first years; but with larger plants, such as are often used in England, it invariably occasioned their roots to strike quickly, by affording a regular supply of moisture, and from being easily permeated by the rootlets, expedited the growth, yielding much early luxuriance when followed by skilful culture, but latterly, seldom to such a degree as would lead us to suppose much difference would be discernible at 30 years of age, between the trenched and those planted by mere pitting, slitting, or sowing,—much more depending on proper draining, on young, thriving, small sturdy plants, of best variety,—on suiting the plant to the soil and climate, and on timely thinning.
But even were a very superior ultimate progress of growth obtained by trenching, manuring, and culture of timber, yet as capital and manure willprobablybe more advantageously employed in common agriculture, which gives a comparatively quick return of both, we shall leave to Mr Withers and his coterie of illuminati the whole advantage of his discovery. Economic philosophy is the queen of our Scottish plants; she will not admit any new system of nurture for her subjects without the{218}strictest scrutiny of its utility as applied to her domains,—she proceeds thus to weigh Mr Withers’s practice:—
Extra Cost per Acre.Twenty loads of putrescent manure, at the average price at which thousands of tons are annually imported to the valley of the Tay fromEngland, 9s. per load,L.900Carriage expenses of above, at 3s. per load,300Twenty loads calcareous manure, including carriage (were marl not at hand, lime would cost thrice as much),400Trenching,900Total first extra cost,L.2500Accumulation by 28 years’ interest, at 5 per cent. nearly,L.10000
Twenty loads of putrescent manure, at the average price at which thousands of tons are annually imported to the valley of the Tay fromEngland, 9s. per load,
Carriage expenses of above, at 3s. per load,
Twenty loads calcareous manure, including carriage (were marl not at hand, lime would cost thrice as much),
Trenching,
Accumulation by 28 years’ interest, at 5 per cent. nearly,
Would land under timber 28 years planted, with growth accelerated by Mr Withers’s practice, in two-thirds of the available portion of Scotland, sell at more than L. 100 per English acre? Suppose that the thinnings previous to the 28th year would cover the cost of planting, and subsequent cultivation and attention which is necessary, besides{219}the cost of the trenching and manuring (in many cases they would not), the entire value of the land would be lost. It may be said that the common rules of utility do not apply in this case,—that the landlords will not be moved to any other improvement than planting, and that otherwise their income would be dissipated entirely, without any portion being applied to reproductive uses. We grant all this; but Scottish landlords have very little taste for the Withers’ system,—to deface their beautiful wastes, by burying all the fine turf and wildflowers under the red mortar (the common subsoil), or to scatter manure. Planting by pitting and slitting will prove far more attractive; besides, the means are entirely awanting to carry on such expensive proceedings to the necessary extent, and the cultivation of one acre in this fashion would leave 19 untouched, when the whole 20 might have been wooded, in many cases to equal advantage, by the money expended on one. We have known planting executed by contract for one year’s interest of the above stated first extra expenditure, which we would match against planting raised by Mr Withers’s process, in the same situation. There is also a very considerable proportion of Scotland very suitable for{220}timber where the stony nature of the surface entirely precludes trenching.
Mr Withers, who appears to have no general knowledge of soils and climates, would hold a different language with regard to Scotland and Scotsmen, if he saw the beautiful thriving plantations now rising in that country, planted by mere pitting and slitting, where, owing to the drought in early summer being less fierce than what occurs in the central, eastern, and southern counties of England, and to the herbage being less luxuriant, planting without trenching can always be depended upon. Mr Withers would also have been sensible had he had much practice in rural affairs, that twenty loads of putrid manure per acre at planting, although of very considerable advantage for two or three seasons to the rising trees, in promoting, along with hoeing and digging, an early start to luxuriance, would cause little or no lasting amelioration of the soil; That the vegetable mould naturally occupying the surface is generally by itself a much better defence against the summer’s drought, than when incorporated with the subsoil, especially after cultivation ceases; that lasting fertility of ground for timber, though sometimes, is often not increased by admixture of soil{221}and subsoil; and that, generally, the luxuriance of the tree must ultimately depend on the natural depth and quality of the ground itself.
Mr Withers, with that precise knowledge of the subject, and clear conception of the nature of things, which generally accompanies a partial acquaintance with facts, makes a confident and rather imposing appearance as a wielder of language and a logician. From his assumed superiority, we especially wonder that he should possibly have envy of Scotsmen, which, from the tenor of his letter, we are constrained to believe. Need Caledonia remind her noble sister, England, of their consanguinity,—that they are sisters whom nature hathtwinnedtogether? Is there another in all the earth, with quadruple the advantages of Scotland, who can rank with her in science and literature, arts and arms? And is England not proud of her poorer sister? Or can they feel aught but mutual love?
Since writing the above, we have looked over some experiments by Messrs Barlow, Beaufoy, Couch, and others, on the strength of timber. These show so much discrepancy of result, as leads us to conclude,{222}that experimenters have not attended sufficiently to the structure and nature of the timber, the position and quality of the different layers, &c. Take, for example, the stem of a tall tree, 100 years old: At the cross section, it is found to consist of a certain number of layers of matured timber, and of sap timber. These layers having been gradually formed, the external, after those more internal have partly dried, and the internal and matured wood being also filled up to more solid consistency than the external, the stem, on being barked, contracts in drying much more externally than internally. As soon as the surface has dried, the outer layers contracting laterally are not sufficient to surround the undried internal layers, thence split in longitudinal rifts; and as the drying proceeds inwards, the cracks deepen till they reach nearly to the heart—these rifts, when the timber is thoroughly dry, being generally wider in the sap timber than in the matured, more than in the proportion of the size of the respective circles. This effect of drying is what every body is acquainted with.
Besides lateral contraction, there is also a disposition to contract longitudinally by drying, much greater in the external than internal layers. While the tree is undivided, this greater contraction of the{223}exterior layers is prevented, by the adhesion to the drier more filled up central column (which probably had contracted a little during the formation of the exterior sap-wood layers), the contractile force of the exterior balancing equally around this central column. Should this balance be destroyed by the stem being cleft up the middle, the longitudinal contraction will immediately take place, and the two halves will bend outward, from the outside layers contracting more than the inside layers. We have seen an ash tree rend up the middle from the cross section above the bulb, nearly to the top, on being cut across in felling, owing to the longitudinal contractile force of the exterior existing even before drying.
Should the dried stem of a tree, of considerable length, be laid hollow, supported at each end, the outside layer being stretched almost to breaking by the longitudinal contraction being greatest in the outermost part, a very small weight, aided by a slight jerk or concussion, may be sufficient to burst the outside layer on the lower side, the outside layers on the upper side not standing out as a support above, but combining their contractile force with gravity to rend the lower. As the outer layer gives way, the strain is thrown concentrated upon the next outermost, which also gives way, and the beam is broken{224}across in detail. In like manner, when the direct longitudinal strength is tested, the external circles being in greater tension than the internal, the tightest parts of the log will give way in succession, like a rope with strands of different degrees of tightness; yet the lateral adhesion of the layers will have considerable effect in strengthening the mass.
The above explains the fallacy of estimating the longitudinal strength of a thick piece of timber from experiments with small shreds; it likewise explains how a large unbuilt mast is so easily sprung; wherefore a beam round as grown will be rendered stronger as a beam by being formed into a hollow cylinder, by boring out the central part; and also how a square log will be strengthened as a beam, by cleaving it up the middle, and placing the two pieces on edge, with their outside or backs together. In the latter case, the middle, by being turned outside, and exposed to the air, will contract more than what it would do shut up and covered by the exterior wood, especially if resinous pine timber, which continues to contract for many years, owing to the resin, when exposed to the air, gradually drying or undergoing some change, by which it is diminished in size, and rendered similar to amber.{225}
Consideration of the difference of tension of the concentric layers, from the difference of disposition to contract by drying, modified by the difference of position in which these layers may stand, when supporting weights and bearing strain, with the various qualities of timber of the same kind of tree, from variety, age, soil, climate, or from being taken from near the outside or heart, or butt or top, will, we think, account for the contrariety of results which unphilosophical experiments have afforded.