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Updated: June 19, 2025
The use of a slit was discarded as unnecessary for objects like the stars, devoid of sensible dimensions, and giving hence a naturally pure spectrum; and a large prism, placed in front of the object-glass, analysed at once, with slight loss of light, the rays of all the stars in the field. Their spectra were taken, as it were, wholesale.
Scheiner's spectrographic researches at Potsdam in 1890 and subsequently, exemplify the immense advantages of self-registration. In a restricted section of the spectrum of Capella, he was enabled to determine nearly three hundred lines with more precision than had then been attained in the measurement of terrestrial spectra.
and is understood to be but a condition of one's own mind, for which, according to the scepticism, latent at least, in so much of our modern philosophy, the so-called real things themselves are but spectra after all.
The numerals might be telegraphed by simple occultations of the light. Then from spectra we might pass by an easy step to equivalent signals of long and short flashes in various combinations, also made by occulting the light. With such a code, our correspondence might go on at great length, and present no difficulty; but, of course, we must be able to reply."
By converging an image of the sun upon a voltaic arc, and thus obtaining the spectra of both sun and arc superposed, he found that the two bright lines which, owing to the presence of a little sodium in the carbons or in the air, are seen in the spectrum of the arc, coincide with the dark lines D of the solar spectrum.
A quantity of stimulus greater than that last mentioned, or longer continued, induces the antagonist muscles into spasmodic action. This is beautifully illustrated by the ocular spectra described in Sect. XL. No. 6. to which the reader is referred.
The first cycle contains 257 plates, all of which have been measured, and a large part of the reduction completed. 8,313 spectra have been measured on them, nearly all of which have been identified, and the places of a greater portion of the stars brought forward to the year 1900, and entered in catalogue form.
In an investigation described by Kirchhoff as "classical," Swan had shown that 1/2,500,000 of a grain of sodium in a Bunsen's flame could be detected by its spectrum. He also proved the constancy of the bright lines in the spectra of hydrocarbon flames.
This has given rise to various conjectures of something floating in the aqueous humours of the eyes; but whoever, in attending to these spots, keeps his eyes unmoved by looking steadily at the corner of a cloud, at the same time that he observes the dark spectra, will be thoroughly convinced, that they have no motion but what is given to them by the movement of our eyes in pursuit of them.
The following examples serve to illustrate the dispersion expressed in this way: Angstrom, Cornu, 10; Draper, photographer of normal solar spectrum, 3.1 and 5.2; Rowland, 23, 33, and 46; Draper, stellar spectra, 0.16; Huggins, 0.1. The most rapid plates are needed in this work, other considerations being generally of less importance.
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