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On the Physical Constitution of the Sun. [Feb. 11, 



The bulbous appearance of the F line before referred to may be taken 

 to indicate violent convective currents or local generations of heat, the 

 condition of the chromosphere being doubtless one of the most intense 

 action. 



4. We will now return for one moment to the hydrogen spectrum. We 

 have already stated that certain proposed experiments have not been carried 

 out. We have postponed them in consequence of a farther consideration 

 of the fact that the bright line near D has apparently no representative 

 among the Fraunhofcr lines. This fact implies that, assuming the line to 

 be a hydrogen line, the selective absorption of the chromosphere is insuffi- 

 cient to reverse the spectrum. 



It is to be remembered that the stratum of incandescent gas which is 

 pierced by the line of sight along the sun's limb, the radiation from which 

 stratum gives us the spectrum of the chromosphere, is very great compared 

 with the radial thickness of the chromosphere itself ; it would amount to 

 something; under 200,000 miles close to the limb. 



Although there is another possible explanation of the non-reversal of the 

 D line, we reserve our remarks on the subject (with which the visibility of 

 the prominences on the sun's disk is connected) until further experiments 

 and observations have been made. 



5. We believe that the determination of the above-mentioned facts leads 

 us necessarily to several important modifications of the received theory of 

 the physical constitution of our central luminary — the theory we owe to 

 Kirchhoff, who based it upon his examination of the solar spectrum. Accor- 

 ding to this hypothesis, the photosphere itself is either solid or liquid, and 

 it is surrounded by an atmosphere composed of gases and the vapours of 

 the substances incandescent in the photosphere. 



We find, however, instead of this compound atmosphere, one which gives 

 us nearly, or at all events mainly the spectrum of hydrogen ; (it is not, how- 

 ever, composed necessarily of hydrogen alone ; and this point is engaging our 

 special attention;) and the tenuity of this incandescent atmosphere is such 

 that it is extremely improbable that any considerable atmosphere, such as 

 the corona has been imagined to indicate, lies outside it, — a view strengthened 

 b}' the fact that the chromosphere bright lines present no appearance of 

 absorption, and that its physical conditions are not statical. 



With regard to the photosphere itself, so far from being either a solid 

 surface or a liquid ocean, that it is cloudy or gaseous or both follows both 

 from our observations and experiments. The separate prior observations 

 of both of us have shown : — 



i. That a gaseous condition of the photosphere is quite consistent with 

 its continuous spectrum. The possibility of this condition has also been 

 suggested by Messrs. De La Hue, Stewart, and Loewy. 



ii. That the spectrum of the photosphere contains bright lines when the 



