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What apology, for instance, will Mr Scott make for the last of these two lines

For when in studious mood he paced

St Kentigern's hall.' Or for these

• How the brave boy, in future war,

Should tame the unicorn's pride.' We have called the negligence which could leave such lines as these in a poem of this nature, inexcuseable ; because it is perfectly evident, from the general strain of his compofition, that Mr Scott has a very accurate ear for the harmony of versification, and that he composes with a facility which must lighten the labour of correction. There are some smaller faults in the diction which might have been as well corrected also : there is too much alliteration, and he reduplicates his words too often. We have ' never, never,' several times; besides ' 'tis o’er, 'tis o'er,'+ in vain, in vain'— 'tis done, 'tis done;' and several other echoes as ungraceful.

We will not be tempted to say any thing more of this poem. Although it does not contain any great display of what is properly called invention, it indicates perhaps as much vigour and originality of poetical genius as any performance which has been lately offered to the public. The locality of the subject is likely to obstruct its popularity; and the author, by confining himself in a great measure to the description of manners and personal adventures, has forfeited the attraction which might have been derived from the delineation of rural scenery. But he has manifested a degree of genius which cannot be overlooked, and given indication of talents that seem well worthy of being enlisted in the service of the epic muse.

The notes, which contain a great treasure of Border history and antiquarian learning, are too long, we think, for the general reader. The form of the publication is also too expensive ; and we hope soon to see a smaller edition, with an abridgement of the notes, for the use of the mere lovers of poetry.

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ART. II. Indagine Fisica su i Colori ; coronata del premio dalla So

cieta Italiana di Scienze. Di Giambattista Venturi, Prof. di Fisica e Presidente del Gabinetto Fisico nell' Univ. di Pavia, della Soc. Ital. di Scienze, &c. &c. &c. Edizione seconda, accresciuta. Modena, An x. Rep. (1801) 8vo.

THE
"he science of Optics, which in the earlier part of the last cen-
tury occupied so much of the attention of physical inquir-

ers,

ers, has of late years yielded its rank, in the estimation of natural philosophers, to the easier, and, perhaps, in themselves more interesting pursuits of the Pneumatic Chemistry. As long as the latter science can be studied without a previous familiarity with the Mathematics, it is to be feared that the high price which must be paid for the delights of the former, will decide mankind to remain in their present state of indifference to its attractions. They will continue to praise the name of Newton for his immor. tal discoveries in this branch of knowledge, without once trying to estimate his merits ; as they have from the beginning worshipped the author of the Principja, without ever imagining that it was a work which was written to be read.

That the knowledge which the “ Treatise of Light' left us of the subtle element which apparently pervades all finite space, fhould, under such circumstances, not have been senGibly augmented since his day, will scarcely appear surprising. In some parts of Europe, however, his sublime researches appear to have attracted more attention than in those where we live. The Italian mathematicians have pursued the investigations left unfinished by him, with an ardour and a success unknown in this country. The two inestimable treatises of Comparetti (not to mention the works of Beccaria) present us with discoveries not less important than those of the opticians who preceded Sir Isaac Newton. We refer our readers in particular to his work i de Luce inflexa et Coloribus, ' published at Ferrara in 1787. It contains matter which deserves a place in the Optics' itself; and only requires to be somewhat extended and pursued in all its consequences, in order to furnish some future philosopher with as ample materials for new discovery, as Newton obtained from the great work of Grimaldi.

The treatise of Professor Venturi, which is now before us, though much inferior in originality and richness of experiment to the book jnft now mentioned, is nevertheless a very valuable acceffion to optical science. It consists of a memoir deservedly crowned by the Societa Italiana, and an additional chapter of great merit. There is an ingenious effay added ' On the means by which we judge of space from the sense of hearing.' This we relerve for another opportunity, and proceed to consider, with some fulness, the optical work.

1. The author begins with a very clear and accurate ftatement of Sir Isaac Newton's fundamental experiment on the coB 3

lours

His other work on Vision and Colours as connected with it, was published in 1798 ; fince which time the author disd.

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lours of thin plates. He then describes the manner in which Du Tour endeavoured to explain this leading phenomenon. That optician conceived the rings of colours and alternate dark intervals to be the result of a limple prifmatic refraction. He fupposed that the first lens acted like a prism, and separated the incident heterogeneous rays, so as to form a coloured spectrum on i he second, from whence it was reflected to the eye placed above both. Professor Venturi adduces no less than five different proofs to thew the insufficiency of this theory. Yet, among all these, it is not a little singular that he omits the most conclusive and the most obvious, viz. the multiplicity of the rings, and the existence of the dark intervals. If common prismatic refraction could produce one image at all resembling a coloured ring in fize or position (which it very certainly never could), we thould still be at a loss to know whence the fucceeding black ring comes, and whence the fecond coloured ring proceeds; not to mention the coincidence of the colouredi rings by transmission with those black spaces by reflexion, and of the black spaces by transmillion with the coloured rings by retlexion. Indeed, it may fairly be conjectured, that he who could propose such as explanation, had neither seen the appearance in question, nor formed any thing like a precise idea of it from Sir Isaac Newton's description : the two phenomena are more dillimitar, in every refpe&, than the colours of thin plates and those of the prisınatic spectrum. We have one other remark to offer on this part of our author's inquiry. He alerts that the term, 'fits of easy and of difficult transmission,' only expresles a fact, and is not of hypothetical origin. It is unqueitio,ably true, that this expres- fion refers to a fact; but it refers to it in a manner purely theo. Tetical; it accounts for, or explains the fact in a way not strictly prescribed by the circumstances, and capable of infinite variations, though those circumstances should remain the same. Nothing, indeed, is advanced repugnant to the phenomenon; but other solutions would agree equally well with it. The problem, for want of sufficient data, is, beyond a certain point, indeterminate ; and one of its many folutions has been adopted. All that the facts warrant us to affert is, that plates of a particular thickness reflect, while those of another degree of thickness transmit light; and that those degrees of thickness which transmit, and those which reflect, succeed each other at certain intervals, the one being as the odd, the other as the even numbers in an arithmetical series. But if we proceed a step farther, and resolve this fact into a transient quality impressed upon the rays of light, which disposes them at one part of their route to be reflected, at another to be transmitted, we surely do some

thing more than merely express the fact on which all these fpeculations are founded, viz. the connexion (of what sort we are ignorant) between a certain thickness of plate, and the reflexion of light; and between another definite thickness, and its transiniffion. Therefore, those philosophers are not so much mistaken as our author imagines, who have denominated the Newtonian theory of fits, an hypothesis. * It would be still more erroneous to call that hypothesis any thing but fine and subtle in the most exquisite degree. We shah afterwards endeavour to trace the steps which led to it.

The remaining part of our author's first chapter is occupied with some remarks upon the different reflexibility of light. It is known to our readers that this property was demonstrated by Sir Isaac Newton from certain experiments with the prism; that by reflexibility, he does not mean a variation in the direction of the reflected rays, but only a power of being reflected at different angles of incidence; and that subsequent inquirers, observa' ing the necessary part which refraction bore in this process, were led to conclude that the different reflexibility of the rays depended upon, and was identical with, their different refrangibility. Professor Venturi examines this position, and endeavours to show by other experiments that it is unfounded. His chief argument is deduced from an experiment performed with a hollow glass vessel filled with water, and containing a plate of glass moveable round one of the angles of the vefiel. He receives a bean on the vessel at right angles to one of its fides, and allows it to pass through the water and fall on the moveable plate, which he inclines to the incident beam until a reflexion begins to take place. He finds that the violet light is first reflected; the red laft; and, because no separation of the rays by refraction could be effected when they fell at right angles, he infers that this different reflexion demonstrates the point in question. The ingenuity of this process, however, cannot close our eyes to its fallacy. Any one who attends to the above abstract of it,

B 4

more

To remove all doubt on this subject, it will be sufficient to subjoi:z Sir Isaac Newton's own words : • Every ray of light acquires, in pai. fing through a refracting surface, a certain tranfient constitution or disa position, which returns at equal intervals during its progress, and makes it, at each return of that difpofition, be easily transmitted through the refracting medium, and in the intervals dispofes it to be easily reflected.' Prop. XII. Book II. Part III.

In the subsequent definition, be denominates those difpofitions fits of easy transmission

1

more especially if he compares it with the author's third figure, will be speedily convinced that he has in fact made use of the very form of experiment described in the third proposition of Sir Isaac Newton's Optics, book I. ; and confequently has added nothing to the evidence of that proposition. The moveable plate forms, together with the anterior Gide of the veffel, a prism, although truncated below. The ingenious contrivance of giving this prism a moveable refracting angle, permits the experiment to proced without changing the incidence of the rays on the anterior surface ; but there is always a second prism joined to the first; and the bare inspection of the third figure shows what a material part it bears in the process. In short, the objections are not in the least removed by this variation of the experiment. Professor Prevost of Geneva, in the Philofophical Transactions for 1798, part II, has given a different and a more satisfactory answer to them, by showing that the refraction of the firit prism ought to render the red rays more reflexible, if all the rays had, independent of the refraction, the same disposition to be reflected. But, in spite of all these reasonings, the radical confideration which first gave rise to the controversy, still recurs : Why does this property, this different reflexibility of light, never appear unless in conjunction with refraction, and in circumstances where the different refrangibility of the rays cannot fail to operate? It is demanded, why a plain mirror of polished metal, upon being moved round its axis, and exposed to the rays at various degrees of inclination, fhews no difference in the different rays? Why, for example, when held at an angle of 80° to the incident beam, is a reflexion produced of the red as well as the violet; and why does the same reflexion continue to take place, although this angle be increased gradually to 79 or 791 degrees, without the flightest appearance of a blue or greenith tinge in the reflected beam, which must inevitably take place if the red and orange part was more transmislible than the violet? It may be said, that the opaque fubftance of the fpeculum reflects all the rays at all angles of incidence. It is therefore admitted, that no light can be absorbed by opaque substances, and that, if the thickness of the speculum be diminished until it becomes tranfparent, all the light will still be reflected.

But let another example be taken, to which no such objection applies. If the rays differ in degree of reflexibility, why does a piece of glass with parallel lides reflect all the component parts of a white beam, equally, at all inclinations to the incident rays ? Why, in this case, is not a separation produced by the reflexion ef the anterior surface when it is inclined at a large angle to the

incident

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