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have mentioned with the highest respect, M. Darracq; and our author now returns to the charge with additional expe.. riments : the result we shall transcribe.
From the experiments which I have related, it appears to be proved,
• Ist. That there exists an affinity between silica and alumina.
• 2dly. That there exists a very powerful affinity between alumina and magnesia.
• 3dly. That alumina shews an affinity for lime; but that the said affinity is not so strong as Mr. Guyton had supposed, nor, if pure reagents be used, is it to be perceived under the circumstances stated by him.
" 4thly. That Mr. Guyton was mistaken in every instance of affinity between the earths, excepting in the case of silica with alumina, which had been observed before his experiments; and that, in the other cases, he has attributed to a cause which does not exist, phenomena that must have resulted from the impurity of his reagents.
5thly. That neither the experiments of Mr. Guyton, nor the opinion maintained in the letter from Freyberg, are sufficient to diminish, in any degree, the value of the assistance mineralogy derives from chemical investigation.' P. 347.
• XI. Description of the Anatomy of the Ornithorynchus Hystrix. By Everard Home, Esq. F.R.S.'
This very singular animal again occurs in a new form, and its anatomy is peculiarly instructive and interesting. The ornithorynchus paradoxus, which seemingly formed a link between the birds and beasts-pretty certainly between the animals of the water and the earth, as the duck did between those of the water and the air-seems to have some conge. ners which merit particular attention. The O, hystrix belongs to the ant-eaters, and is noticed in the Zoology of Dr, Shaw (whose Lyncean eyes nothing escapes), under the name of myrmecophaga aculeata. This naturalist observes that it forms the link between the ant-eaters and the porcupines. It approaches also the manis; but this animal is found to be further removed from the ornithorynchus than the ant-eater: Even the myrmecophagæ are decidedly mammalia.
· The peculiar characters of the ornithorynchus, as a genus, or more properly a tribe of animals, are,
• The male having a spur on the two hind legs, close to the heel. · The female having no nipples.
• The beak being smooth, while the rest of the animal is covered with hair.
· The tongue having horny processes, answering the purposes of teeth.
• The penis of the male being appropriated to the passage of the semen; and its external orifice being subdivided into several openings, so as to scatter the semen over an extent of surface, while the urine passes by a separate canal into the rectum.
The female having no common uterus; and the tubes which correspond to the horns of the uterus in other quadrupeds, receiving the semen immediately from the penis of the male.
• These characters distinguish the ornithorynchus, in a very remarkable manner, from all other quadrupeds, giving this new tribe a resemblance in some respects to birds, in others to the amphibia; so that it may be considered as an intermediate link between the classes mammalia, aves, and amphibia ; and, although the great difference that exists between it and the myrmecophaga, the nearest genus we are at present acquainted with, shows that the nicer gradations towards the more perfect quadrupeds are not at present known, the facts which have been stated may induce others to prosecute the inquiry, and render that part of the chain more complete.
• Between it and the bird, no link of importance seems to be wanting.' P. 360.
Another species of ornithorynchus was shot at Van Diemen's Land : it greatly resembled the (). bystrix.
XII. A Method of examining refractive and dispersive Powers, by prismatic Reflection. By William Hyde Wollaston, M. D. F.R.S.'
Our author's method may be styled, in a great measure, new : it is at least new in its application. It depends on the principle of Newton's prismatic eye-glass; viz. the reflexion of light at the inner surface of a dense refractive medium.
. Since the range of inclination within which total reflection takes place, depends not only on the density of the reflecting prism, but also on the rarity of the medium adjacent to it, the extent of that range varies with the difference of the densities of the two mcdia. When, therefore, the refractive power of one medium is known, that of any rarer medium may be learned, by examining at what angle a ray of light will be reflected from it.
For instance, when any object is laid under a prism of Aint-glass, with air alone intei posed, the internal angle of incidence at which the visual ray begins to be totally reflected, and at which the object ceases to be seen by refraction, is about 39° 10°; but, when the object has been dipped in water, and brought into contact with the glass, it continues visible, by means of the higher refractive power of ihe water, as far as 571° of incidence. When any kind of oil, or any resinous cement, is interposed, this angle is still greater, according to the refractive power of the medium employed; and, by cements that refract more strongly than the glass, the object may be seen through the prism, at whatever angle of incidence it is viewed.
• In examining the refractive powers of fluids, or of fusible substances, the requisite contact is easily obtained; but, with solids, which can in few instances be made to touch to any great extent, this cannot be effected without the interposition of some fluid, or cemen?,
of higher refractive power than the medium under examination. Since the surfaces of a stratum so interposed are parallel, it will not effect the total deviation of a ray passing through it, and may therefore le employed without risk of any error in consequence.
i Thus, resin, or oil of sassafras, interposed between plate glass and any other prism, will not alter the result.
• If, on the same prism, a piece of selenite and another of plateglass be cemented ncar each other, their powers may be compared with the same accuracy 23 if they were both in absolute contact with it.
• For such a mere comparison of any two bodies, a common triangular prism is best adapted; but, for the purpose of actual measurement of refractive powers, I have preferred the use of a square prism, because, with a very simple apparatus, it shows the sine of refractive pouver sought, without the need of any calculation.' P. 365.
This mode of measuring the refractive power is often useful in determining the genuineness of substances, since those of the same kind possess this property, with little variation. The first table contains a series of substances, arranged according to their refractive powers,
The second section of this paper relates to the dispersion of light, which is regulated by very diferent laws from refraction, since, at å given incidence, bodies may refract unequally and disperse equally. When different media, in contact, differ greatly in dispersive power, the usual order of prismatic colours may be reverseit. They are found to be so, by the application of oil of sassafras to a prisın of flint glass. Numerous similar instances are mentioned; and the second table contains a series of substances, in the order of their dispersive powers, both in water and alcohol. The soJutions of the morc perfect metals possess the greatest power of this kind, particularly the nitrates; yet sulphuret of potash rises above the muriate of iron, the nitrate of silver and copper: oil of sassafras disperses light very powerfully; but the effect of some other essential oils, in this respect, is much more inconsiderable. The least dispersive metal is zinc. A third table contains a series of substances with their refractive and dispersive powers, ascertained by means of edges, in the manner of Mr. Dollond and Dr. Blair. These, however, are less distinct; and the results, in some measure, difler. With respect to the colours of the spectrum, our author is not inclined to reduce them to three: yet, by employing a very narrow pencil of light, he sees four ouly ; vit. red, yellowish-green, blue, and violet ; but in this there is apparently a deception. He points out also the existence of invisible rays beyond the violet, such as Herschel supposes to esist on this side the red. Our author's test is blackening
the muriate of silver. With these two kinds of invisible rays, be thinks the whole number to be six.
• XIII. On the oblique Refraction of Iceland Crystal. By William Hyde Wollaston, M. D. F.R.S.'
Our author's theory on this subject cannot be very intelligibly abridged. It is connected with Euler's doctrine of light, which he supposes to be propagated by the vibrations of a highly elastic medium.
• In ordinary cases, the incipient undulations are of a spherical form ; but, in the Iceland crystal, light appeared to Huygens to pro-, ceed as if the undulations were portions of an oblate spheroid, of which the axis is parallel to the short diagonal of an equilateral piece of the crystal, and its centre the point of incidence of the ray.
• From this spheroidical form of the undulations, he deduces the obliquity of refraction; and lays down a law, observable in all refractions, at any surface of the spar, whether natural or artificial, which bears the closest analogy to that which obtains universally at other refracting surfaces; for as, in other cases, the ratio is given between the sine of incidence and sine of refraction, (or ordinate of the spherical undulation propagated,) so, in the Iceland crystal, the ratio betweer the sine of incidence and ordinate of refraction (in any one section of the spheroidical undulation) is a given ratio.' P.382.
As this system is wholly inconsistent with light as a chemical principle, and, we think, with its other phænomena; 've shall not enlarge on it. Better arguments than have been hitherto offered in favour of Euler's hypothesis must be adduced, before we can attend minutely to the application.
• XIV. An Account of some Cases of the Production of Colours, not hitherto described. By Thomas Young, M.D. F.R.S. F.L.S. Professor of Natural Philosophy in the Royal Institution.'
We find it impossible to analyse the present article with any tolerable success. It depends also on Euler's theory. The cases of colours before us arise from those of fibres, and of mixed plates ; but many of the facts appear to us to be explicable on the principles of other systems.
We cannot conclude this volume without esceeding the space to which we inust confine ourselves, as M. Prevost's paper alone would detain us too long. We shall return to it very soon.
(To be continued.)
ART. III. — The IVorks of Virgil, translated into English
l'erse by Mr. Dryden. A new Edition, revised and corrected by John Carey, LL. D), 3 Vols. So. 11. 78. Boards. Vernor and Hood. 1803.
IT is an ample proof of the intrinsic excellence of Drv: den's translation, that, - notwithstanding the variety of versions of the Roman bard, which either in whole or in part have since been offered to the public, and the advantages which the diferent translators have enjoved, as well froin his defects as his meritshe has hitherto never been supplanted. If he have not always maintained a pre-eminence, he has, at least, never sunk below the level of his artagonists: he has never ceased to be treated with veneration occasionally, indeed, with idolatry. Yet the translation of Dryden was ushered into the world under circumstances the most discouraging and unpropitious. The veteran poet had exceeded his grand climacteric when he first published his proposals to finish it in three years: be became extremely indolent for the first twelvemonth of the period to which he had confined himself, and can scarcely be said to have made even a beginning; and the natural cousequence was, that lie was compelled to outvie even Lucilius himself, in rapidity of composition-stans pede in uno—and to trust to the printer to correct the errors both of the copy and the press. Hence few publications have been more disfigured with inaccuracies of every description, than the first edition of this version, which bears the date of 1697; and, although a new edition was demanded, and made its appearance about a twelvemonth afterwards, the critical hoe was applied with a most lazy hand, and but few of the weals irere removed from the heavily encumbered soil. The translator had already found the work to answer his purpose, and was satisfied with the fame and the profit it had procured him.
· These' (observes the present editor) were the only editions printed in Dryden's life-time. The third, published in 1709, is merely a servile though not faithful copy of the second, and was committed to the press without the trouble of ever consulting the first, except once, for the purpose of doing mischief, in Æn. vii, 146. As to the subsequent publications, they plainly appear to have been each copied from the last preceding, as each preserves all the errors of its immediate predecessor, with the addition of a new crop of its own
• In speaking thus freely of the past editions, I am far froni wish. ing to insinuate that the present is in all respects perfect: I am suffi. ciently sensible that it is not, and that much yet remains to be done. All, therefore, that I venture to hope from my feeble efforts, is, that the work may, in its present state, be deemed soinewhat less