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yond the requirements of the church; he possessed a remarkable memory; his reading was extensive; he spoke and wrote Latin with elegance and ease; he had a considerable knowledge of Greek; he wrote both Italian and Latin verse; he was devoted to music; he had a fine ear, and a melodious voice which had been cultivated with assiduous care; in the august ceremonies of the Catholic Church, he was always distinguished for the splendor of his dress, and the dignity and decorum of his manner. Bayle, in his "Historical Dictionary," article Leo X., says: "Men of letters, of what religion or nation soever, are bound to praise and bless the memory of this pope, for the care he took to recover the manuscripts of the ancients; he spared neither pains nor cost in searching for them and procuring very good editions. Guicciardini, in the first twelve books of his history, represents Leo X. as an accomplished model of modern policy, and the greatest statesman of his age." Rankes, in his "History of the Popes,"* in speaking of Leo X., says: "A liberal kindness, active intellect, a ready persuasion of good in others were among his distinctive characteristics. These qualities are the fairest gifts of nature, and but rarely acquired, but when possessed, how greatly do they enhance all life's enjoyments.'

We cannot better conclude this article than in the language of Mr. Roscoe, the elegant biographer of Leo X.

"That an astonishing proficiency in the improvement of the human intellect was made during the pontificate of Leo X. is universally allowed. That such proficiency is principally to be attributed to the exertions of that pontiff will now perhaps be thought equally indisputable. Of the predominating influence of a powerful, an accomplished, or a fortunate individual on the character and manners of the age, the history of mankind furnishes innumerable instances; and happy is it for the world when the pursuits of such individuals, instead of being devoted, through blind ambition, to the subjugation or destruction of the human race, are directed towards those beneficent and generous ends, which, amidst all his avocations, Leo X. appears to have kept continually in view."

ART. VII.-1. Philosophical Magazine; Ed. by A. TILLOCH. London, 1798-1822.

2. London and Edinburgh Philosophical Magazine and Journal of Science; Ed. by SIR D. BREWSTER. Taylor and Phillips: London, 1832-1850.

Vol. i., p. 68, Bohn's edition.

3. London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science; Ed. by KANE AND FRANCIS. London, 1851.

4. Denkschriften der Königlichen Academie der Wissenschaften zu München für die Jahre 1814, 1815. München: 1817.

5. Abstracts of the Papers printed in the Philosophical Transactions of the Royal Society of London. London: R. and J. E. Taylor. 6. L'Institut, Journal Universel des Sciences, &c. Paris.

7. Annales de Chemie. Paris.

8. Annalen der Physik und Chemie. Von J. G. Poggendorff. Leipzig.

Of all natural phenomena, none are more striking than the production of the rainbow. Iris, the divine token of the Greeks and Romans, was especially pointed out to man by the God of the Hebrews: "I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth." When, by an artificial production of the rainbow effect, we enable ourselves to understand that the remote orbs, not only of our solar system but of others, are composed of the same elements which combine to constitute our globe, and from thence deduce the existence of him who called our attention to this natural spectrum, we fail not to read this promise again with renewed hope.

*

As might be expected, the list of authors who have discussed this phenomenon is very long; they belong to many nations and to almost all ages; but it is to Fletcher, who, in 1571, first announced refraction of the sunlight by the rain to be the cause, and to De Dominis,† Descartes, and Newton, that we owe theories and experimental investigations, culminating in the true explanation of the effect. It is only necessary here to allude to the labors of Newton, which laid the foundation of this branch of analysis. It is not known positively who first separated a ray of white light into its constituent colored rays, by refracting it with an artificial prism.

In 1666, Newtont performed this experiment to amuse himself, using a triangular glass prism; but his amusements turned out to be of more importance to mankind than the most recondite researches, in this direction, of previous

* Priestly on Light and Colors, p. 50.

† De Radiis Visus et Lucis, 1611.

Optics. London, 1718, p. 22.

philosophers. He first drew conclusions worthy of the striking effect produced. He announced that different rays of light have different degrees of refrangibility, and that to the same degree of refrangibility always belongs the same color, and to the same color the same degree of refrangibility. In studying the solar spectrum, he pointed out the advantages of a slit, with its length parallel to the prism, for the beam to pass through, suggesting one an inch or two long and or of an inch wide, or even narrower, and described the effects of circular or triangular openings.

Pownall called attention in 1801, to Herschel's statement in 1796, that the colored rays of the sunlight do not proceed from that globe itself, but from inflamed vapors floating on its surface. It occurred to him that similar colored lights arising from flames of bodies burnt in our terrestrial atmosphere should be found to observe the same refractions and be affected by the same laws which operate in the solar light. By direct analogy he supposes the solar light to be emitted from a compound of inflamed vapors, each colored ray therein taking the hue of its respective vapor-flame, and refers to these colored vapors being produced in the sun by the inflammation of the same bodies which can produce them here.

These speculations interest us as being the results of one of the earlier attempts to analyse the sun's constituents. He describes the spectra of the electric spark, iron filings in oxygen, phosphorus in oxygen, camphor dissolved in alcohol, spermaceti in Argand's lamp, wax, and tallow. He uses the spectrum of red-hot iron as his standard. This, viewed through a prism, is found decomposed into a deeply tinged red and a deep bluish green only, the gradations of blue being invisible. His apparatus consisted of a high, long box, black internally, with a sliding door in front, pierced with a half-inch hole. A side door admitted the lights to be examined. The prism was applied to the hole. In studying blue flames, removing the hole, he turned his prism till the beam was refracted on the floor of his darkened room. "This solar light must arise, he says, from vapors having similar bases as these terrestrial colored lights have"-" and must, having the same properties, be of the same nature" -"it is resolved exactly as the terrestrial lights above examined are, into the constituent colored lights which the

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several bases give out." He speculates on the mineralogy of the sun, moon, and stars, from facts concerning the various lights they emit.

Wollaston observes, in 1802, that by looking through a prism at a distant crevice in a window-shutter, the division of the spectrum may be seen much more distinctly than by any other method. In the light of the lower part of a candle, the spectrum is distinguished by dark spaces into five distinct portions. This latter observation is the scaffolding for the first story of the edifice whose foundations Newton laid.

It is to Fraunhofer,† (1815) that we owe our first description of the nature of these dark spaces, though he was ignorant of their cause and importance. In his paper he gives instructions in the art of examining spectra formed with combinations of prisms and viewed through a telescope. He calculated the angles of refraction of the colored rays for prisms of various substances, and described the apparatus used, which consisted essentially of the lights examined with their accompanying slit and prism in one house, and across the street in another house a second prism and telescope. He called attention to the effect of temperature in altering the results he made a long and very narrow slit in the window-shutter, and near it placed an equiangular flintglass prism. Twenty-four feet off, with a telescope, he viewed the spectrum from a lamp, and noticed what was afterwards called the line of sodium. He was entirely ignorant of the profound importance this observation was destined to assume. With the same apparatus, observing the solar spectrum, he observed it crossed by very many dark lines of various breadths and shades. He gave a plate of this result, in which we count three hundred and fifty-five lines perpendicular to the length of the spectrum, and it is especially to be noted that he figures the sodium line, before alluded to, as a double line. The most marked lines he calls A, a, B, C, D, (double, afterwards called sodium line), E, b, F, G, H. The intervals vary greatly between these lines themselves, and the natural groups into which they are arranged.

To observe these phenomena in their perfection, the prism must be placed at its angle of minimum deviation. Oil of anise is recommended as the refracting medium.

He

Phil. Mag., vol. xiii., p. 289.

+ Denkschrift. der Königlich. Akad. der Wissenschaft. zu München. Band v. 193.

measured the angles of refraction of B, C, D, E, F, G, and H. These lines ever afterwards bore the name of Fraunhofer's fixed lines, and to him credit is undoubtedly due for establishing the second epoch in what was to become the modern spectral chemical analysis. He studied, with his apparatus, beams from Sirius, Venus, and other celestial bodies, comparing their spectra with the solar, and noticed how the spectra of the stars differed one from another.

It is not necessary here to give details; they will be given further on when we review the discoveries which extend the observations, made by modern physicists with perfected apparatus, in celestial chemistry. He described the spectrum of electric light, which differed from that of the sun and of artificial fires. Static electricity was passed through a glass tube between two conductors, and a dark line was seen in the green part of the spectrum, one in the orange, one in the red, and four others in the violet portions. This is the nucleus of some of the most brilliant of modern investigations. He examined the spectrum of hydrogen and of alcohol, noticing that the reddish-yellow line of the spectrum of each was the brightest he fails to recognise it in sulphur. These experiments are very significant to us now.

In 1822, Herschel analysed the light from the colored flames emitted by various ignited bodies, by means of the prism. He described the spectra of compounds of strontia, lime, copper, and boron. In 1827,† he also described the spectra of lithium, iron, and barium. "Of all salts," he says, "the muriates succeed best from their volatility;" "the colors thus communicated by the different bases to flame, afford in many cases a ready and neat way of detecting extremely minute quantities of them."

Talbot, in 1826, analysed the spectra of various artificial lights. He observed a constant yellow ray for all the salts of sodium, and a red ray, of low but definite refrangibility, characteristic of salts of potassium. "If," he says, "this opinion should be correct and applicable to the other definite rays, a glance at the prismatic spectrum of a flame may show it to contain substances which it would otherwise require a laborious chemical analysis to effect." This was prophetic. In 1834, he described the difference

* Edin. Phil. Trans., v. Miller Chem. Phys. Encycl. Metrop., p. 438.

Brewster's Journ. of Science, vol. v., v. Miller, Chem. Phys. § L. & E. Phil. Mag. & Journ. of Sc., vol. iv., p. 114.

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