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THE NATIONAL REVIEW.
Art. 1.—LIGHT AND SUNLIGHT. Chemical Analysis by Spectrum Observations. By Professors Kirch
hoff and Bunsen, of Heidelberg. Philosophical Magazine for Au
gust 1860, 4th Ser. vol. xx. p. 89. On the Relation between the Radiating and Absorbing Powers of
different Bodies for Light and Heat. By G. Kirchhoff. Ibid.* Lecture at the Royal Institution of Great Britain, Friday, March
1st, 1861: On Bunsen and Kirchhoff's Spectrum Observations. By H. E. Roscoe, Esq., Professor of Chemistry in Owens College,
Manchester. Report in the Journal of the Institution. Light is our chief servant in the getting of knowledge, infinitely more swift and subtle than the Magician's servant, Ariel. We think of things almost solely as Light informs us about them, and the sound, feeling, and smell of things are but tacked on to our visual notions of them. And through the eye, as through a window, it is said, we look into the souls of others. By Light also, Nature reveals to us her endless forms of beauty, and the landscape, from some elevated point, fills us with undescribed feelings. And as we use telescopes and microscopes of ever-increasing power, it is still by Light we learn the evergreater and the ever-less.
It is well to remind the reader of the past and present services of Light to knowledge, because some exact students of Nature, never contented, are about to impose upon their servant new and, if possible, more refined duties than before.
Translated from Poggendorff's Annalen, vol. cix. p. 275. No. XXV. July 1861.
Chemists, like others, have long used their eyesight to distinguish one object or substance from another by its colour, crystalline shape, or kind of surface. And if, to be more sure, they tried experiments upon a substance, it was but to transmute it into other shapes and colours, of which light again informed them. But we now find that by light we may look a substance through and through, and see every kind of atom in it. We are, it seems, to keep an instrument by us; and to learn what a thing is made of, we need only drop a particle of it into a flame, and then look through a telescope. Written up in lines of many-coloured light we see the natural sign and name of every element that happens to be present, even though the quantity of matter which thus makes its presence known does not exceed the 1,000,000th or the 100,000,000th of a grain. The public has heard a great deal about clairvoyance and second-sight, but now we are truly to become clairvoyants, and see into the very composition of matter.
In such terms we may without much inaccuracy introduce this discovery of spectrum-analysis, a method of observing the components of substances which is literally as plain as daylight. All who know what the prismatic spectrum is will understand at the mere suggestion how the process works, but other readers may require some short preliminary explanation. Any ordinary ray of light, especially white light, consists of innumerable simple rays of light, commonly referred to as the colours of the rainbow, and used as the most descriptive expression for numberless variety. As we ordinarily receive light, these innumerable rays are fused together, and their distinctive colours merge by composition into some one tint, or into common white light, such as the sun so bountifully pours down upon us. It is only by this compound ray that in ordinary life we recognise things, and every one knows what a great deal we may do in this way. Optical philosophers, however, from the time of the great Newton, had been aware that we may separate the compound ray of light, and examine each component separately. Passing the ray through a prism, a simple piece of pure glass, with two inclined plane faces, the whole ray indeed is refracted or bent from its course towards that side on which the glass is thicker. But Newton found that every two rays differing in colour or kind are bent in a different degree. Thus, however numerous the rays which a compound beam of light contains, we have only to pass it through a prism, and the whole are laid out in the most perfect order in a band of brilliant rainbow hues, known as the spectrum. When proper precautions are taken, nothing can express the perfection with which the rays of light are thus sifted out according to their nature. If we conceived dust composed of particles of every size to be let fall into a steady wind, it