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But the nebulae have other affinities not until recently suspected; for the spectra of some of them are practically identical with the spectra of certain comets. The conclusion seems warranted that comets are in point of fact minor nebulae that are drawn into our system; or, putting it otherwise, that the telescopic nebulae are simply gigantic distant comets. Lockyer's Meteoric Hypothesis
By virtue of this quality, purple served from antiquity for the vesture of those who have reached the highest stage of human development for their time. This characteristic of the middle colours of the two spectra was expressed by Goethe when he called green 'real totality', and peach-blossom 'ideal totality'. From this standpoint Goethe was able to smile at the Newtonians.
With Thalèn, he besides added manganese, titanium, and cobalt to the constituents of the sun enumerated by Kirchhoff, and raised the number of identical rays in the solar and terrestrial spectra of iron to no less than 460. Thus, when Sir Norman Lockyer entered on that branch of inquiry in 1872, fourteen substances were recognised as common to the earth and sun.
With lateral light the colour is compounded of the reverse spectrum of the central object, and the direct spectrum of the circumjacent objects, in proportion to their respective quantity and brilliancy. Variation and vivacity of the spectra occasioned by extraneous light.
Blue emissions of the Wolf-Rayet type then became occasionally prominent, in remarkable correspondence with the varying lustre of the star; finally, a band at Lambda 3969, found by Wright at Lick to characterise nebular spectra, assumed abnormal importance; and in July the nebular transformation might be said to be complete. Striking alterations of colour attended these spectral vicissitudes.
With some modification I have on a former occasion used the following words regarding the precursors of the discovery of spectrum analysis, and solar chemistry: 'Mr. Talbot had observed the bright lines in the spectra of coloured flames, and both he and Sir John Herschel pointed out the possibility of making prismatic analysis a chemical test of exceeding delicacy, though not of entire certainty.
Shortly afterwards, Professor Langley, then director of the Allegheny Observatory, having devised a means of comparing with great accuracy light from different portions of the sun's disc, found that while the obscure rays in two juxtaposed spectra derived from the solar poles were absolutely continuous, no sooner was the instrument rotated through 90°, so as to bring its luminous supplies from opposite extremities of the equator, than the same rays became perceptibly "notched."
By 1868 Huggins had satisfactorily examined the spectra of about seventy nebulæ, of which one-third displayed a gaseous character. All of these gave the green ray fundamental to the nebular spectrum, and emanating from an unknown form of matter named by Sir William Huggins "nebulum."
The effort to discover a meaning in the pictures led to the fusion of this image with one of the subjective spectra, and in this way the idea of a Hamlet frontispiece probably arose. The whole process of dream-construction is clearly illustrated in a curious dream recorded by Professor Wundt.
We are reminded that they are elliptical in outline, which accords with the hypothesis; that their spectra are not gaseous, which shows that they may be composed of solid particles like the planetesimals; and that their central masses present an oval form, which is what would result from the tidal effects, as just described.
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