FOOTNOTES:
[84] “These—oxygen, hydrogen, nitrogen, and carbon—are the four bodies, in fact, which, becoming animated at the fire of the sun, the true torch of Prometheus, approve themselves upon the earth the eternal agents of organisation, of sensation, of motion and of thought.”—Dumas, Leçons de Philosophie Chimique, p. 100. Paris, 1837.
[85] It will be found in examining any of the works of the alchemists,—particularly those of Geber, De inveniendi arte Auri et Argenti, and his De Alchemiâ; Roger Bacon’s Opus Majus, or Alchymia Major; Helvetius’ Brief of the Golden Calf; or Basil Valentine’s Currus Triumphalis,—that in the processes of transmutation the solar light was supposed to be marvellously effective. In Boyle’s Sceptical Chemist the same idea will be found pervading it.
Amid all their errors, the alchemists were assiduous workmen, and to them we are indebted for numerous facts. Of them, and of their age, as contrasted with our own, Gibbon remarks:—“Congenial to the avarice of the human heart, it was studied in China, as in Europe, with equal eagerness and equal success. The darkness of the middle ages ensured a favourable reception to every tale of wonder; and the revival of learning gave new vigour to hope, and suggested more specious arts of deception. Philosophy, with the aid of experience, has at length banished the study of alchemy; and the present age, however desirous of riches, is content to seek them by the humbler means of commerce and industry.”—Decline and Fall, vol. ii. p. 137.
[86] On the two theories the following maybe consulted:—Young, Supplement to Encyclopædia Britannica, article Chromatics; Fresnel, Supplément à la Traduction Française de la 5ième édition du Traité de Chimie de Thomson, par Riffault, Paris, 1822; Herschel’s Article, Light, in the Encyclopædia Metropolitana, and the French Translation of it by Quetelet and Verhulst; Airy’s Tract on the Undulatory Theory, in his Tracts, 2nd edition, Cambridge, 1831; Powel, The Undulatory Theory applied to Dispersion, &c. p. 184; Lloyd’s Lectures, Dublin, 1836–41; Cauchy, Sur le Mouvement des Corps élastiques, Mémoires de l’Institut, 1827, vol. ix. p. 114; Théorie de la Lumière, Ibid. vol. x. p. 293; M’Cullagh, On Double Refraction, Ibid., vol. xvi.; Geometrical Propositions applied to the Wave Theory of Light, Ibid., vol. xvii.; Sir David Brewster’s papers in the Transactions of the Royal Society of Edinburgh, and the Philosophical Magazine.
[87] Results of Astronomical Observations made during the years 1834–38, at the Cape of Good Hope, &c. By Sir John Herschel, Bart., K.H., D.C.L., F.R.S.—“In the contemplation of the infinite, in number and in magnitude, the mind ever fails us. We stand appalled before this mighty spectre of boundless space, and faltering reason sinks under the load of its bursting conceptions. But, placed as we are on the great locomotive of our system, destined surely to complete at least one round of its ethereal course, and learning that we can make no apparent advance on our sidereal journey, we pant with new ardour for that distant bourne which we constantly approach without the possibility of reaching it. In feeling this disappointment, and patiently bearing it, let us endeavour to realise the great truth from which it flows. It cannot occupy our mind without exalting and improving it.”—Sir D. Brewster: North British Review.
[88] For examples of this, consult Graham’s Elements of Chemistry; Brande’s Manual of Chemistry; or, indeed, any work treating of the science. The formation of ink, by mixing two colourless solutions, one of gallic acid and another of sulphate of iron, may be taken as a familiar instance.
[89] Sir John Herschel, in his paper On the Chemical Action of the Rays of the Solar Spectrum on Preparations of Silver, remarks that, “it may seem too hazardous to look for the cause of this very singular phenomenon in a real difference between the chemical agencies of those rays which issue from the central portion of the sun’s disc, and those which, emanating from its borders, have undergone the absorptive action of a much greater depth of its atmosphere; and yet I confess myself somewhat at a loss what other cause to assign for it. It must suffice, however, to have thrown out the hint; remarking only, that I have other, and, I am disposed to think, decisive evidence (which will find its place elsewhere) of the existence of an absorptive solar atmosphere, extending beyond the luminous one. The breadth of the border, I should observe, is small, not exceeding 0·5 or 1/7 part of the sun’s radius, and this, from the circumstances of the experiment, must necessarily err in excess.”—Philosophical Transactions, 1840.
[90] Experiments and Observations on some Cases of Lines in the Prismatic Spectrum, produced by the passage of Light through Coloured Vapours and Gases, and from certain Coloured Flames. By W. A. Miller, M.D., F.R.S., Professor of Chemistry in King’s College, London.—Philosophical Magazine, vol. xxvii.
[91] Report on the Mollusca and Radiata of the Ægean Sea, and on their distribution, considered as bearing on Geology. By Edward Forbes, F.R.S., &c.—Reports of the British Association, vol. xii. Professor Forbes remarks:—“A comparison of the testacea, and other animals of the lowest zones, with those of the higher, exhibits a very great distinction in the hues of the species, those of the depths being, for the most part, white or colourless, while those of the higher regions, in a great number of instances, exhibit brilliant combinations of colour. The results of an enquiry into this subject are as follows:—