Catalogue Entry: OTHE00126

^[1] Part iii., Prop. viii. ix., &c.

^[2] Probably Sulphate of Barytes.

^[3] Optics, Book ii., Part iii., Prop. x.

^[4] See Transactions of the Geological Society, 2d Series, vol. iii. p. 455; and North British Review, vol. xviii. p. 227.

^[5] Journal Book of the Royal Society.

^[6] It was published in the Phil. Trans. 1671, p. 2039.

^[7] Traité de Lumière, chap. v. p. 57 ; and Maseres' Scriptores Opticæ, p. 234.

^[8] Query 25th and 26th at the end of the work.

^[9] The term unusual, and the ratio of the sines, viz. 5 to 3, were given by Bartholinus in the abstract of his Paper in the Phil. Trans., No. 67, Jan. 1670-1, pp. 20, 39.

^[10] Traité de Mineralogie, tom. i. p. 159, Note.

^[11] Hauy's Elements of Nat. Phil., by Gregory, vol. ii p. 337.

^[12] See Appendix, No. III.

^[13] Correspondence, &c. pp. 264-273. From the originals in the British Museum, Add. MSS., 4237, fol. 32 and 34.

^[14] Hooke's Collections, March 1682, No. 6, p. 167.

^[15] The Thalami Nervorum Opticorum.

^[16] Briggs considers this muscle necessary to prevent squinting, by "keeping the eye even and in sight." — Hooke's Coll., March 1682, p. 170.

^[17] Dated Trin. Coll. Cambridge, September 12, 1682. Appendix, No. IV.

^[18] Descartes himself distinctly states that we see objects single with two eyes in exactly the same way as we feel objects single with two hands, forgetting that we see them double by the displacement of the coincident images, and never feel them double by the two hands. See Descartes' Dioptrice, cap. 6, De Visione, Art. X. The experiment of feeling a pea double between two fingers, is not hostile to this observation.

^[19] This is precisely the theory of Rohault, see p. 229.

^[20] This letter contains, as will be seen in the Appendix, No. IV., a paragraph respecting the opinions of a Mr. Sheldrake, who, as Mr. Edleston informs us, was a Fellow of Corpus Christi College, and seven years senior to Newton. Mr. Sheldrake <224> states that vision is more distinct when the eye is directed to the object, than when the object is above or below the optic axes. I do not recollect that this curious fact has been stated by any previous writer on vision.

^[21] See Appendix, No. V.

^[22] Dated Cambridge, May 1685.

^[23] The one the Theory of Vision, and the other his Ophthalmographia. Cantab. 1676, and Lond. 1687.

^[24] See Appendix, No. VI.

^[25] See Appendix, NO. VII.

^[26] Although it is evident, from a careful perusal of the 15th Query, that it contains the same doctrine of the semi-decussation of the optic nerves which is given in the MS., yet it has been misunderstood by Dr. Reid, who obviously had not seen the copy of it in Harris's Optics. "Sir Isaac Newton," says Dr. Reid, (Inquiry, cap. vi. sect. 13), "who was too judicious a philosopher and too accurate an observer to have offered even a conjecture which did not tally with the facts which had fallen under his observation, proposes a query with respect to the cause of it, (namely, the relation and sympathy between corresponding points of the two retinæ.)" — Optics, Query 15. Dr. Reid seems not to have detected the doctrine of semi-decussation in the Query, and to have believed that individual nerves, not half-nerves, from the two sides of both eyes, united before they reached the brain, and there produced a joint and single impression; and Dr. Alison has either taken up Dr. Reid's opinion, or misunderstood the Query, and also the theory of semi-decussation. "It is well-known," he says, "that an explanation (of single vision by means of double images) was proposed by Newton, fully considered by Reid, and since supported by Wollaston, (often called the theory of Wollaston, but quite incorrectly,) proceeding on the supposition of a semi-decussation of the human optic nerves at their commissure, whereby the fibres from the right half of the retina go to the right optic lobe in the brain, and vice versa." This is the theory of Rohault, and not of Newton and Wollaston, in which the half-fibres, from the right half of the retina of each eye, unite into one fibre at their commissure GH in Fig. 12, and then go to the right optic lobe.

^[27] Sir Isaac draws other four conclusions from his theory, but they will find a fitter place in the Appendix, No. VIII.

^[28] A Latin translation of Rohault's work was published in 1708, by Dr. Clarke, "with annotations chiefly from the philosophy of Newton, and yet no notice is taken of Newton's Theory, as contained in his l5th Query, although Dr. Clarke had translated the Optics into Latin. He adds a note stating, that the conjecture <230> respecting the fibres of the optic nerve had not yet been confirmed by dissection. Part I. cap. 31, p. 225, note.

^[29] The suffusio dimidians of other authors

^[30] See Transactions of the Medical and Physical Society of Calcutta, vol. ii. p. 151; or Edinburgh Journal of Science, July 1828, vol. ix. p. 143.

^[31] Wagner's Handwörterbuch der Physiologie, vol. iii. part ii. p. 297.

^[32]

If by the sense of touch we could make the two images appear one, then we should also see an object single when it is doubled by looking either at a nearer or a more distant object, or when it is made 100 by a multiplying glass; but if a man were to live a 1000 years, he would still see the two or the hundred images, though he knew there was only one object. In order to illustrate his opinion, Dr. Brown says that the two English words he conquered, excite the same idea as the one Latin world vicit. In reply to this Dr. Whewell says, "that to make this pretended illustration of any value, it ought to be true that when a person has thoroughly learned the Latin language, he can no longer distinguish any separate meaning in he and in conquered." With this assertion we cannot concur. The two words he conquered un <232> doubtedly convey the same meaning as vicit. If we unite the two words thus, heconquered or conqueredhe, we cannot doubt that the word he is as truly included in the termination it of vicit, as he is in the single word heconquered, unless it is alleged that vicit may also mean she conquered.

Dr. Brown's real mistake consists in not taking two exactly similar words, as vicit, vicit, like what he considers as the two exactly similar images. The two words pronounced in succession convey certainly only one idea, but the mind recognised the same in succession or its duplicity, just as it would do the two similar and united images, if one of them were slipped from its superposition on the other by pressing aside one of the eye-balls.

Dr. Brown's views are affected with another error, namely, in the assumption that the pictures in each eye are exactly similar.

^[33] Edinburgh Transactions, vol. xiii. p. 479.

^[34] There is no opposition between the impressions on the concave retina and on a concave surface of the body. If we hold up the hand vertically, and bend it into a concavity, an impression made on the upper part of the concavity, will be felt as coming from below, and an impression on the lower part of the concavity will be felt as coming from above, exactly as in the case of the concave retina.

^[35] We have not noticed the additional explanation adopted by Dr. Alison, "that impressions on the upper part of the retina are impressions on the lower part of the optic lobes, i.e., of the sensorium;" because he has not told us what requires as much explanation as inverted vision, namely, why the lower part of the sensorium makes the object seem lower! Is the sensorium a plane, or a convexity, or a concavity ? If it is a concavity, a physical impression on the lower part will correspond to the top of the object, and an impression on the upper part with the bottom of it.

^[36] I omit all consideration of the question, whether the choroid coat or retina is the seat of vision, or whether the foramen centrale is or is not an opening in the retina.

^[37] See Edinburgh Transactions, vol. xv. p. 360.

^[38] When a ray falls obliquely upon the retina (or any other surface of sensation) its action may be decomposed into two, the one lying in the surface of the membrane, and acting laterally upon the papillæ, and the other perpendicular, and acting in the direction of the axis of the papillæ, and therefore passing to the brain.

^[39] See Edinburgh Transactions, vol. xv. pp. 350-353, and North British Review, vol. xvii. p. 165.

^[40] Experiments and Considerations touching Colours, chap. ii. § 9, p. 19. Lond. 1664.

^[41] King's Life of Locke, vol. i. pp. 404-408. Edit. 1830.

^[42] Art. Accidental Colours, in the Edinburgh, Encyclopædia, vol. i. pp. 91, 92.

^[43] See Phil. Trans., 1742-43, vol. xlii. p. 155.

^[44] Phil. Trans. 1731, p. 147.

^[45] Sprot's Hist. of the Royal Society, p. 246. Lond. 1667.

^[46] The Posthumous Works of Robert Hooke, M.D., p. 503, tab. xi. fig. 2. Lond. 1705. In the description given of it by Waller, his biographer, the invention is mentioned as "an instrument for taking angles at one prospect, which he found described on a loose paper."

^[47] Grant's Hist. of Physical Astronomy, p. 487; and Nautical Mag. vol. i. p. 351.

^[48] See Edinburgh Journal of Science, vol. vi. p. 61; Encyclopædia Brit., Art. Microscope, vol. xv. p. 41.

^[49] Newtoni Opera, tom. iv. p. 300.

^[50] Sir Isaac does not seem to have afterwards described this construction.

^[51] See Edinburgh Transactions, vol. ix. p. 433; and the Edinburgh Journal of Science, July 1829, No. I. new series, p. 108.

^[52] See Newtoni Opera, tom. iv. p. 276.

^[53] Treatise on Optics, edit. of 1853, p. 404.

^[54] It is a curious fact, that "there is the same peculiarity about the preface to the Principia{.}" — Edleston's Correspondence &c. &c., pp lviii and lxxi.

^[55] " Probably Slaughters' Coffee-house in St. Martin's Lane." — Edleston's Correspondence, p. lxxiv.

^[56] Eloge, by Fontenelle. — Mém. Acad. Par. 1727. Hist. p. 151.

^[57] The English edition was reprinted at London in 1717, 1721, and 1730, and the Latin one at London in 1719, 1721, 1728, at Lausanne in 1740, and at Padua in 1773.

^[58] Biographia Brit. Art. Newton, vol. vii. p. 779.

^[59] An analysis of the Lectiones Opticæ has been given by the author of the Life of Newton in the General Dictionary, vol. vii. p. 779, note; but it is by some mistake confined to the first Part, as if there were no second Part. The same mistake is committed in the Biographia Britannica, vol. v. p. 3215, note, where it is obvious that the author knew nothing of the second Part, as he calls the last portion of the first Part the "Last Section of these Lectures."