Imágenes de páginas
PDF
EPUB

parallel case in time. We observe the daily formation of rounded pebbles by the action of the waves on fragments of rock on the sea-shore; and we find the incessant continuance of that action for a long time give rise to accumulated beds of shingle.

Now, over large tracts of land, at considerable elevations above the sea, we find immense beds of pebbles presenting precisely the same appearance of rolled and rounded fragments, as those we now observe in the progress of formation in the sea. It is, then, by the same process of reasoning which connects the gravitation of a stone with that of the moon, or the remotest planet or comet, that we connect the formation of beds of pebbles at the present day with that of similar beds in ages of remote antiquity, when the present dry land formed the bottom of the ocean; or, rather, was gradually emerging from it, through such a long succession of ages as would alone suffice for the production of the immense beds of rolled gravel which we find deposited over a large part of the surface of the globe.

Philosophical induction, then, proceeds mainly by seizing upon analogies between known orders of facts, known relations of cause and effect, and cases where the existence of such relations is unknown, but where the circumstances render it probable that they also subsist. Such circumstances, perhaps quite casual and unimportant in the eyes of the ordinary observer, suggest in an instant, to the practised mind of the philosophical inquirer, a train of relations in which the analogy is maintained. He proceeds to verify his idea: a single experimental instance often suffices to confirm it; and at most, a very few repetitions and variations in the circumstances and conditions, satisfy him that his analogy is correct, and the uniformity of the law by which physical action is determined becomes established.

In fact, so essential to induction is the dependence on analogy, that in the very use of the terms, “observation,” “ experience,” and the like, by many writers, to describe the grounds of our belief in physical events, it is evident that they mean to include essentially the reference to analogy, and not barely to facts actually witnessed. Unless this be the case, indeed, their meaning would in some cases be involved in absurdity and contradiction.

Thus, then, the most important part of the process of induction consists in seizing upon the probable connecting relation by which we can extend what we observe in a few cases to all. In proportion to the justness of this assumption, and the correctness of our judgment in tracing and adopting it, will the induction be successful. The methods by which a facility in discovering such relations, and a readiness in forming such judgment, may be attained and improved, are precisely the objects

principally to be kept in view by the philosophical student who would prepare himself for the work of interpreting the phenomena of the natural world. The analogies to be pursued must be those suggested from already-ascertained laws and relations. This, in proportion to the extent of the inquirer's previous knowledge of such relations subsisting in other parts of nature, will be his means of guidance to a correct train of inference in that before him.

And he who has, even to a limited extent, been led to observe the connexion between one class of physical truths and another, will almost unconsciously acquire a tendency to perceive such relations among the facts continually presented to him. The truth of the remark to which we have been thus led is amply confirmed by the history of philosophical discovery.

In point of fact, discoveries, commonly termed inductive, have very seldom been really attained by the mere process of amassing collections of individual facts. It has been almost invariably the case that hypothesis has preceded observation; and that the discoverer has in truth only verified, by an appeal to experiment, the general theory which he had already imagined. The happy selection of such hypotheses is that which characterizes, and in fact constitutes, philosophical genius. And a just appreciation of the use of such imaginary provisional assumptions, eminently distinguishes the rational inquirer from the speculative visionary. The true philosopher neither discards hypothesis on the one hand, nor yields himself up to it on the other; but rates it at its proper value, and turns it to its legitimate use. He is always ready to reject an assumed theory the moment he finds it unsupported by fact : but if it be once duly substantiated, to adopt it, and be prepared to follow it out into all its legitimate consequences, however at variance with received notions,—however contrary to established prejudices,however opposed to the prepossessions, the bigotry, the cherished delusions of mankind.

And the more extensive his acquaintance with nature, the more firmly is he impressed with the belief that some such relation must subsist in all cases, however limited a portion of it he may be able actually to trace. And it is by the exercise of an unusual skill in this way, that the greatest philosophers have been able to achieve their triumphs in the reduction of facts under the dominion of general laws.

But important as these natural analogies are to the philosopher, they are yet of a nature which renders it difficult to make them generally appreciated : and, unless by actual and attentive study of physical science, it would probably be a hopeless task to attempt to convey an adequate conception of the irresistible claim to acceptance with which they present themselves to the mind of a person even moderately versed in such inquiries. Yet they are, in fact, no more than extensions of the very same elements of thought, which seem implanted in our nature; by which all our acquaintance with sensible objects is, in the first instance, acquired; and by which we are continually and unconsciously storing our minds with that knowledge, which is so necessary for all the purposes of our existence ;—those natural persuasions upon which all uniform convictions, and all consistent conduct is based ;--and without which life would be a continued state of infancy.

But it is not, perhaps, until we come to contemplate natural phenomena, exhibited in the form of numerical results, and find those data reducible to mathematical laws, that we fully appreciate the reality and exactness of that uniformity by which all nature works. The coincidence with such laws, is that which, above all others, impresses us with the conviction of invariable order and uniformity pervading the material universe. VOL. I.

z

5

nomena.

We find this, in the first instance, in the reduction of vast collections of observed numerical results, under simple mathematical laws. But the more extended application of mathematical analysis powerfully augments the impression produced on our minds by the conspiring inductions, and corroborating generalizations, of purely physical investigations. From some

one very simple, remote, and abstract datum, obtained from elementary physical facts, we often proceed by purely mathematical reasoning, perhaps through a long and intricate deduction, which at length brings us to the conclusion, that, under certain conditions, a particular kind of action ought to take place; and even the precise amount of its effects ought to be such as are given by a certain analytical expression. The results of observation exactly accord with these deductions; and even the minutest variations in the effects are exactly represented by calculation from the formula of theory.

We have occasionally singular exemplifications of the existence of recondite principles of analogy, in the coincidence of phenomena with the symbolical indications of mathematical analysis. A mathematical formula is found, which expresses the law of a certain class of phe

The analytical language of symbols admits, perhaps, of certain changes, or embraces certain cases, not at all contemplated in the first numerical establishment of the law; but dependent purely upon abstract algebraical rules and transformations. These symbolical changes shall be found to have physical cases exactly corresponding to them.

Of this, we have the most striking instances in optics. We may cite the simple case of the law of refraction; whence, by a mere abstract algebraical change, the substitution for the numerical refractive index, of the fictitious abstraction (-1), we obtain another formula, which is no other than the law of reflection, and a whole series of formulas, expressing all the consequences of that law, corresponding to those of the law of refraction.

In the higher departments of physical optics, the same thing has been most surprisingly exemplified. We need only cite the marvellous prediction of the conversion of plane into circular polarization of light, by two internal reflections in glass, made and verified by M. Fresnel, entirely upon the strength of certain mechanical and mathematical analogies. “A conclusion," (as Professor Forbes justly remarks,) 56 which no general acuteness could have foreseen; and which was founded on the mere analogy of certain interpretations of imaginary expressions. The mere reasoner about phenomena could never have arrived at the result,—the mere mathematician would have repudiated a deduction founded upon analogy alone."--(On “ Polarization of Heat," Edinb. Trans. Vol. xiii.)

BOTANICAL RAMBLES IN THE VICINITY OF DOVOR.

No. I. The increasing taste for botanical pursuits, and the wish, now so generally shown, of gaining an acquaintance with our native Flora, has induced me to draw up the following account of a few rambles in search of plants, which I made in the vicinity of Dovor, last autumn, and in the autumn of 1833.

Dovor, with its magnificent and far-famed cliffs, its venerable and imposing castle, its sea-views, so beautiful and full of animation, is very justly admired, and a numerous set of visiters annually assemble there in the summer and autumn. To many of these, I hope my rambles will be useful, if not interesting, and will serve to point out certain spots, where, during their walks, they may find many of our pretty and interesting native plants.

In visiting a new neighbourhood, I have often had to regret the want of such an aid, -particularly when my time has been short ;-and, supposing others

may have the same feelings, I with less hesitation take up this subject, which may appear to some so trifling.

I do not aim at a correct list of all the plants found in the vicinity of Dovor, many must have escaped me,-and the early spring plants I have had no opportunity of observing ;-however, I hope that there will be a sufficient number noticed, to give a tolerable idea of the character of the flora.—For further information on the plants of this part of the coast, G. E. Smith's Catalogue of the Plants of South Kent may be consulted, and the localities of many very interesting and rare plants will be found there detailed. I will here observe, that many of the more common plants will not be mentioned, as the list, by so doing, would only be enlarged, without rendering any service to the reader. In my names I follow Hooker,-considering his British Flora to be more generally used than any other at the present time. His work may be referred to for ascertaining the time of flowering, or other facts the reader may require, as I shall merely give the names of the plants, with here and there a remark.

The best method, I think, of pointing out the localities, will be to request the reader to go over the ground again with me; but before we proceed on our first ramble I may be perhaps allowed to state, for the information of those who do not know the nature of the soil and country about Dovor, that it is entirely chalk, forming, inland, a series of rounded undulations and downy steeps, and, towards the sea, breaking into a line of fine and bold cliffs. This line is intersected, at Dovor, by a valley, in which the town, and several small villages, are situated, with the road to Canterbury running along a great part of its length. To the eastward of Dovor, the cliffs continue in one unbroken line for about three miles; then they sink to a mere bank at St. Margaret's, but immediately afterwards show themselves again. To the westward, the line, commencing at Archcliff Fort, continues unbroken to Lydden-spout, a distance of about two and a half miles; here it sweeps inland, at a small distance from the sea, and proceeds on towards Folkstone, almost disappearing before it reaches that town. By the sweeping of the cliffs inland, at Lydden-spout, a most beautiful but miniature undercliff is formed, which I consider the most lovely spot in the neighbourhood, and one possessing peculiar attractions to the botanist, from the number of interesting plants found there. Beautiful and secluded as this spot is, still it is condemned to be spoiled by a railroad, which will pass along its whole length, and ruin it for ever. Advocate as I am for railroads, it is with deep regret I see this favourite spot about to be destroyed. At the foot of the cliffs, in many places, there are sloping banks, some of considerable magnitude, formed, apparently, by the gradual crumbling away of the face of the cliff. In other places, the sea washes up to the face of the cliff at high tide, leaving no kind of communication, and, therefore, rendering the passing of such spots about high-water somewhat dangerous.

We will now prepare for a ramble, and our first expedition shall be from the town, under the castle-cliffs, to the zig-zag path leading up to the station-house, and thence we will return home along the top of the cliffs and through the castle-meadow.

As soon as we get clear of the houses, we shall come to a series of sloping banks with the cliff rising perpendicularly behind them. This spot is quite a botanic garden; and, with due search, we shall discover the following plants, some of which, however, will require a little climbing to gather, as they grow high up on the banks, near the face of the cliff. Hard Meadow Grass (Poa rigida), Devil's-bit Scabious (Scabiosa succisa), Field Knautia (Knautia arvensis), Yellow Bed-straw (Galium verum), Hoary Plantain (Plantago media), Bucks-horn Plantain (Plantago coronopus), Wall Pellitory (Parietaria officinalis), Common Vipers' Bugloss (Echium vulgare), Common Centaury, (Erythræa centaurium), Autumnal Gentian (Gentiana amarella), Common Burnet Saxifrage, (Pimpinella saxifraga), Samphire (Crithmum maritimum), Common Wild Parsnep (Pastinaca sativa), Sea Beet (Beta maritima), Upright Spiked Thrift (Statice spathulata), Perfoliate Yellow-wort (Chlora perfoliata), Great Hairy Willow-herb (Epilobium hirsutum), Small-flowered Hairy Willow-herb (Epilobium parviflorum), Nottingham Catchfly (Silene nutans), Sea Spurrey Sandwort (Arenaria marina), Dyer's Rocket (Reseda luteola), Bare Rocket, or Wild Mignonette (Reseda lutea), Yellow Horned Poppy (Glaucium luteum), Common Marjoram (Origanum vulgare), Self-heal (Prunella vulgaris), Common Eye-bright (Euphrasia officinalis), Common Vervain (Verbena officinalis), Clove-scented Broom-rape? (Orobanche caryophyllacea), Sea Cabbage (Brassica oleracea), Fine-leaved Mustard (Sinapis tenuifolius), Sand Mustand (Sinapis muralis), Common Kidney Vetch (Anthyllis vulneraria), Hawk-weed Picris (Picris hieracioides), Dwarf Plume-thistle (Cnicus acaulis), Common Hempagrimony (Eupatorium cannabinum), Ploughman’s Spikenard (Conyza squarrosa), Common Golden-rod (Solidago virgaurea), Greater Knapweed (Centaurea scabiosa), Spreading Halbert-leaved Orache (Atriplex patula).

Among the foregoing plants I may remark that the common vipers' bugloss sometimes grows here in a very unusual way, the leaves being densely clothed with long hair-like bristles, and the spikes of flowers apparently abortive, and consisting of a mass of whitish-green bristles, giving them somewhat the appearance of those excrescences on the rosetree, caused by the puncture of an insect. The variety of leaf exhibited by the common burnet saxifrage, will often puzzle a young botanist, and

« AnteriorContinuar »