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Moreover, both the dark solar and the bright terrestrial "D lines" were displayed by the refined Munich appliances as double. In this striking correspondence, discovered by Fraunhofer in 1815, was contained the very essence of solar chemistry; but its true significance did not become apparent until long afterwards. Fraunhofer was by profession, not a physicist, but a practical optician.
Fraunhofer, who initiated the study of the diffraction spectrum, used a real grating of very fine wires: but rulings on glass were adopted by his successors, and were by Nobert executed with such consummate skill that a single square inch of surface was made to contain 100,000 hand-drawn lines.
Here it was assumed that the missing rays were stopped, and here also it was assumed that the missing rays would be seen bright, could they be isolated from the overpowering splendour of their background. This isolation is effected by eclipses, with the result beautifully confirmatory of theory of reversing, or turning from dark to bright, the Fraunhofer spectrum.
In conjunction with the celebrated Fraunhofer he made disks of nine or ten inches in diameter, which were employed by his colaborer in constructing the telescopes which were so famous in their time. He was long supposed to be in possession of some secret method of avoiding the difficulties which his predecessors had met.
Here the work of English instrumental artists was for the first time rivalled, and that of English opticians when Fraunhofer entered the new establishment far surpassed. The development given to the refracting telescope by this extraordinary man was indispensable to the progress of that fundamental part of astronomy which consists in the exact determination of the places of the heavenly bodies.
"People are born with the moral or with the material bias; uterine brothers with this diverging destination: and I suppose, with high magnifiers, Mr. Fraunhofer or Dr. Carpenter might come to distinguish in the embryo at the fourth day, this is a whig and that a free-soiler." Let us see what Emerson has to say of "Power:" "All successful men have agreed in one thing they were causationists.
Yet this need occasion no surprise when we remember that the Fraunhofer spectrum integrates the absorption of multitudinous strata, various in density and composition, while only the upper section of the formation comes within view of the sensitive plates exposed at totalities, the low-lying vaporous beds being necessarily covered by the moon.
But if reflected sunshine, it was objected, the chief at least of the dark Fraunhofer lines should be visible in it, as they are visible in moonbeams, sky illumination, and all other sun-derived light. The objection was well founded, but was prematurely urged, as we shall see.
Wollaston, but they were afterwards multiplied and measured by Fraunhofer with such masterly skill, that they are now universally known as Fraunhofer's lines. To give an explanation of these lines was, as I have said, a problem which long challenged the attention of philosophers, and to Professor Kirchhoff belongs the honour of having first conquered this problem.
Kirchhoff formed a spectrum of the limelight, and after the two bright lines had vanished, he placed his salt flame in front of the slit. The two dark lines immediately started forth. Thus, in the continuous spectrum of the lime-light, he evoked, artificially, the lines D of Fraunhofer.
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