What apology, for inftance, will Mr Scott make for the laft of thefe two lines We have called the negligence which could leave fuch lines as these in a poem of this nature, inexcufeable; because it is perfectly evident, from the general ftrain of his compofition, that Mr Scott has a very accurate ear for the harmony of verfification, and that he compofes with a facility which muft lighten the labour of correction. There are fome fmaller faults in the diction which might have been as well corrected alfo : there is too much alliteration; and he reduplicates his words too often. We have never, never,' feveral times; befides '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 fay any thing more of this poem. Although it does not contain any great difplay 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 fubject is likely to obftruct its popularity; and the author, by confining himself in a great measure to the defcription of manners and perfonal adventures, has forfeited the attraction which might have been derived from the delineation of rural fcenery. But he has manifefted a degree of genius which cannot be overlooked, and given indication of talents that feem well worthy of being enlisted in the fervice of the epic mufe. 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 alfo too expenfive; and we hope foon to fee a fmaller edition, with an abridgement of the notes, for the ufe of the mere lovers of poetry. ART. II. Indagine Fifica fu i Colori; coronata del premio dalla Societa Italiana di Scienze. Di Giambattista Venturi, Prof. di Fifica e Prefidente del Gabinetto Fifico nell' Univ. di Pavia, della Soc. Ital. di Scienze, &c. &c. &c. Edizione feconda, accrefciuta. Modena, An x. Rep. (1801) 8vo. THE HE fcience of Optics, which in the earlier part of the last century occupied fo much of the attention of phyfical inquir ers, ers, has of late years yielded its rank, in the estimation of natural philofophers, to the eafier, and, perhaps, in themfelves more interefting pursuits of the Pneumatic Chemistry. As long as the latter fcience 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 prefent ftate of indifference to its attractions. They will continue to praise the name of Newton for his immortal difcoveries in this branch of knowledge, without once trying to estimate his merits; as they have from the beginning worshipped the author of the Principia, without ever imagining that it was a work which was written to be read. That the knowledge which the Treatife of Light' left us of the fubtle element which apparently pervades all finite fpace, fhould, under fuch circumftances, not have been fenfibly augmented fince his day, will fcarcely appear furprising. In fome parts of Europe, however, his fublime refearches appear to have attracted more attention than in those where we live. The Italian mathematicians have purfued the investigations left unfinished by him, with an ardour and a fuccefs unknown in this country. The two inestimable treatifes of Comparetti (not to mention the works of Beccaria) prefent us with difcoveries not lefs important than those of the opticians who preceded Sir Ifaac Newton. We refer our readers in particular to his work de Luce inflexa et Coloribus,' published at Ferrara in 1787.* It contains matter which deferves a place in the Optics' itself; and only requires to be fomewhat extended and purfued in all its confequences, in order to furnish fome future philofopher with as ample materials for new discovery, as Newton obtained from the great work of Grimaldi. The treatife of Profeffor Venturi, which is now before us, though much inferior in originality and richness of experiment to the book just now mentioned, is nevertheless a very valuable acceffion to optical fcience. It confifts 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 fenfe of hearing.' This we referve for another opportunity, and proceed to confider, with fome fulness, the optical work. I. The author begins with a very clear and accurate statement of Sir Ifaac Newton's fundamental experiment on the co His other work on Vifion and Colours as connected with it, was publifhed in 1798; fince which time the author died. lours of thin plates. He then defcribes 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 refult of a fimple prifmatic refraction. He fuppofed that the first lens acted like a prifm, and feparated the incident heterogeneous rays, fo as to form a coloured spectrum on the fecond, from whence it was reflected to the eye placed above both. Profeffor Venturi adduces no lefs than five different proofs to thew the infufficiency of this theory. Yet, among all thefe, it is not a little fingular that he omits the most conclufive and the most obvious, viz. the multiplicity of the rings, and the existence of the dark intervals. If common prifmatic refraction could produce one image at all refembling a coloured ring in fize or pofition (which it very certainly never could), we fhould ftill be at a lofs to know whence the fucceeding black ring comes, and whence the fecond coloured ring proceeds; not to mention the coincidence of the coloured rings by tranfmiflion with thofe black fpaces by reflexion, and of the black spaces by tranfmiflion with the coloured rings by reflexion. Indeed, it may fairly be conjectured, that he who could propofe fuch an explanation, had neither feen the appearance in queftion, nor formed any thing like a precife idea of it from Sir Ifaac Newton's defcription: the two phenomena are more diffimilar, in every refpect, than the colours of thin plates and thofe of the prifinatic fpectrum. We have one other remark to offer on this part of our author's inquiry. He aflerts that the term, fits of eafy and of difficult tranfmiffion,' only exprefies a fact, and is not of hypothetical origin. It is unquestionably true, that this expreffion refers to a fact; but it refers to it in a manner purely theoretical; it accounts for, or explains the fact in a way not strictly prefcribed by the circumstances, and capable of infinite variations, though thofe circumstances fhould remain the fame. Nothing, indeed, is advanced repugnant to the phenomenon; but other folutions would agree equally well with it. The problem, for want of fufficient 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 thofe of another degree of thickness tranfmit light; and that thofe degrees of thickness which transmit, and thofe which reflect, fucceed each other at certain intervals, the one being as the odd, the other as the even numbers in an arithmetical feries. But if we proceed a ftep farther, and refolve this fact into a tranfient quality impreffed upon the rays of light, which disposes them at one part of their route to be reflected, at another to be tranfmitted, we surely do fome thing more than merely exprefs the fact on which all thefe fpeculations are founded, viz. the connexion (of what fort we are ignorant) between a certain thickness of plate, and the reflexion of light; and between another definite thicknefs, and its tranfmiffion. Therefore, thofe philofophers are not fo much mistaken as our author imagines, who have denominated the Newtonian theory of fits, an hypothefis. * It would be still more erroneous to call that hypothefis any thing but fine and fubtle in the most exquifite degree.-We fhall afterwards endeavour to trace the steps which led to it. The remaining part of our author's first chapter is occupied. with fome remarks upon the different reflexibility of light. It is known to our readers that this property was demonstrated by Sir Ifaac Newton from certain experiments with the prifm; 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 fubfequent inquirers, obferving the neceffary part which refraction bore in this procefs, were led to conclude that the different reflexibility of the rays depended upon, and was identical with, their different refrangibility. Profeffor Venturi examines this pofition, and endeavours to fhow by other experiments that it is unfounded. His chief argument is deduced from an experiment performed with a hollow glafs veffel filled with water, and containing a plate of glass moveable round one of the angles of the veffel. He receives a beam on the veffel 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 feparation of the rays by refraction could be effected when they fell at right angles, he infers that this different reflexion demonftrates the point in queftion. The ingenuity of this process, however, cannot clofe 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 fufficient to fubjoin Sir Ifaac Newton's own words: Every ray of light acquires, in paffing through a refracting furface, a certain tranfient conftitution or dif. pofition, which returns at equal intervals during its progrefs, and makes it, at each return of that difpofition, be eafily tranfmitted through the refracting medium, and in the intervals difpofes it to be eafily reflected.' Prop. XII. Book II. Part III. In the fubfequent definition, be denominates thofe difpofitions fits of eafy tranfmiffion. more especially if he compares it with the author's third figure, will be fpeedily convinced that he has in fact made ufe of the very form of experiment defcribed in the third propofition of Sir Haac Newton's Optics, book I.; and confequently has added nothing to the evidence of that propofition. The moveable plate forms, together with the anterior fide of the veffel, a prism, although truncated below. The ingenious contrivance of giving this prifm a moveable refracting angle, permits the experiment to proced without changing the incidence of the rays on the anterior furface; but there is always a fecond prifm joined to the first; and the bare infpection of the third figure fhows what a material part it bears in the process. In fhort, the objections are not in the leaft removed by this variation of the experiment. Professor Prevost of Geneva, in the Philofophical Tranfactions. for 1798, part II, has given a different and a more fatisfactory anfwer to them, by fhowing that the refraction of the first prifm ought to render the red rays more reflexible, if all the rays had, independent of the refraction, the fame difpofition to be reflected. But, in fpite of all these reasonings, the radical confideration which firft gave rife to the controverfy, ftill 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 polifhed metal, upon being moved round its axis, and expofed 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 fame reflexion continue to take place, although this angle be increafed gradually to 79 or 79 degrees, without the flighteft appearance of a blue or greenith tinge in the reflected beam, which muft inevitably take place if the red and orange part was more tranfmiflible than the violet? It may be faid, 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 abforbed by opaque fubftances, and that, if the thicknefs of the fpeculum be diminished until it becomes tranfparent, all the light will ftill be reflected. But let another example be taken, to which no fuch objection applies. If the rays differ in degree of reflexibility, why does a piece of glafs with parallel fides reflect all the component parts of a white beam, equally, at all inclinations to the incident rays? Why, in this cafe, is not a feparation produced by the reflexion of the anterior furface when it is inclined at a large angle to the incident |