1868.] 



Constitution of the Sun and Stars. 



3 



phenomena of the luminous clouds ; and it will avoid contusion in this part 

 of our investigation to adopt provisionally the definite hypothesis that the 

 central body of the sun is an opake ocean with a highly reflecting surface — 

 such a surface as an untarnished white molten alloy would present. We 

 shall run no risk of error in doing this if we afterwards carefully reexamine 

 such parts of our inquiry into the phenomena of the clouds as would be 

 affected by substituting for this hypothesis any other that is admissible. 



5. [We shall also assume that the photosphere is not itself the origin of 

 the heat which it disperses abroad, but draws it from the adjoining regions. 

 No doubt if chemical action could be the source of solar heat, the photo- 

 sphere might be its seat, and resemble the luminous part of a candle- 

 flame. In this case the opaque regions within might be cooler than the 

 photosphere, provided the photosphere were so translucent as to allow a 

 sufficient radiation through it from the parts within to the open sky. But 

 the photosphere to be thus translucent should of necessity be at a far 

 higher temperature than an equally bright body with a perfectly radiating 

 surface. And almost to this intense heat it would raise a great extent of 

 the outer atmosphere, which, being eminently transparent, is but imper- 

 fectly fitted to moderate the heat it receives from contact with the photo- 

 sphere. Hence we should expect to see conspicuous bright lines in the 

 solar spectrum, which, however, we do not find. Moreover, the amount of 

 the sun's radiation appears to be decisive against our attributing it to 

 chemical action. — September 1868.] 



6. Let us consider what would happen if the photosphere were away, and 

 nothing but an atmosphere of fixed gases in contact with an intensely heated 

 molten sphere. To simplify our conceptions, let us conceive the molten 

 mass to have a core which is maintained at a constant temperature, to 

 have a surface reflecting perfectly, and to be enveloped by an extensive 

 atmosphere of one fixed gas, which, for further simplicity, we shall sup- 

 pose gives a spectrum of invariable lines. The atmosphere is supposed to 

 be extensive enough to render the change of temperature throughout it so 

 gradual that there are no currents of convection. The under surface of 

 this atmosphere would be raised by direct contact to the same temperature 

 as the polished surface of the dark body within. The temperature would 

 very slowly decrease in passing outwards from the core, first through the 

 molten ocean, and then through the atmosphere, until that upper layer of the 

 atmosphere was reached which alone can emit heat into space. Through the 

 thickness of this outer stratum the temperature would rapidly fall, the whole 

 escape of heat from the system taking place exclusively from it, in the form 

 of undulations of the ether of those particular wave-lengths which the gas 

 constituting the atmosphere can excite. Such is a picture of what would ulti- 

 mately become the permanent state of such a system as we have imagined. 



7. Let us now suppose the surface of the ocean to lose part of its re- 

 flecting-power, and to become such an imperfect mirror as is possible with 

 the bodies we know to exist. The surface of the ocean will at once begin 



b 2 



