[1870. DOUGLAS — ON OBSERVATIONS OK THE SUN. 12!) 



really interrupted ; it is merely darkened through the narrowing 

 of the bright interspaces by reason of the bulging of the dark rays 

 and the formation of a number of cloudy lines. Many of these 

 cloudy lines correspond with those observed in the spectrum of the 

 sun, when on the horizon ; and certain lines in the red orange 

 space are identical with those produced by a cirrus cloud crossing 

 the field of view, and, therefore, indicate the existence of watery 

 vapor. A careful comparison of their spectra has led Father 

 Secchi to the conclusion, that, as the spectra of the red orange 

 stars and the spectra of the solar spots are identical, the sun, 

 stripped of its chromosphere, would resemble Alpha in Orion, or 

 micron in the Whale ; as it is, it is a variable star. The layer 

 of absorbing vapor, which, by its varying thickness and density, 

 produces this variation, is denser on the spots. The questions 

 then arise: is it piled up at such points above the average level of 

 the chromosphere ? — or, does it fill cavities in the photosphere ? 

 The Rev. Father inclines to the latter opinion. He finds, more- 

 over, that in the spectrum of the spot, the iron and calcium lines 

 are more strongly marked than the magnesium and sodium ; 

 hence, he concludes that the former metals, existing at the bottom 

 of the cavity, mark the dark nucleus of the spot : the latter are 

 within the region of the penumbra. Eemark that this opinion 

 difi"ers materially from the old view, wdiich supposed the dark 

 nucleus to be the dark body of the sun — the penumbra to be the 

 sides of the cavity. It approaches nearly the old notion that the 

 spots arc caused by a dowurush of a cool, absorbing atmosphere 

 upon the visible body of the sun, — only, according to recent 

 observations, the downrush fills cavities in the gaseous body 

 of the sun. This gaseous body, under such pressure as exists 

 there, emits white light, which is more largely absorbed in tlio 

 spot than elsewhere, because there the absorbing medium — viz., 

 the vapors and gases which fill the cavity — forms a deeper and 

 denser layer than elsewhere. 



As I said before, the subject requires further elucidation ; 

 and in its further investigation, Capt. Ashe's theory of falling 

 asteroids being elements in the disturbance which takes place in 

 the region of a spot, is certainly worthy of consideration ; for, 

 although the theory requires remodelling to suit new facts, some 

 of the data on which it rests cannot be overlooked. 



The old cavity theory, which he long ago showed the absurdity 

 of, has been abandoned by all, and the new cavity theory, wliicli 



