THE REVOLUTIONS OF THE CRUST OF THE EARTH. 285 



tutle north aud south, while the protuberances appear in all latitudes,* 

 this particular proof loses its force. 



Furthermore, Warren de la Rue has brought absolute proof to the 

 support of the existence of a cavity in the spots. Two photographs of 

 the sun, taken with an interval of two days between them, and united in 

 a stereoscope, give clearly the perception of a cavity. 



These considerations, and many others, cause us to prefer the hypoth- 

 esis of Wilson, Herschel, and Arago, who admit the existeuce of a pho- 

 tosphere of a cloudy envelope, aud an opaque iuterior.t 



It remains for us to inquire what is the nature of this interior ; is it 

 solid, liquid, or gaseous? In what way does the sun produce the enor- 

 mous amount of heat it has given forth from immeasurable time? 

 And how are produced the spots whose origin has been explained in 

 such different ways? 



A close observation of the formation of the spots, and of the phenom- 

 ena which precede and follow them, has furnished Mr. Faye with the 

 elements of his hypothesis, in which he declares that the solar mass is 

 entirely gaseous, because the ascending currents which produce the 

 spots proceed from very great depths in the solar mass, and conse- 

 quently that it is the contraction of this gaseous mass, which furnishes 

 the enormous heat radiated into space. 



The extension of the same phenomena to all the stars, and to all mat- 

 ter in course of formation, raises the value of this hypothesis which, 

 however, does not claim to be perfect. It is in fact only a sketch, made 

 by the* hand of a master, which still requires some touches of the pencil 

 to make it a complete picture, embracing in its generalities the cosmic 

 life of matter. Let us consider the hypothesis more in detail. 



There exist gaseous masses of a temperature superior to all chemical 

 affinity. This great heat is produced by the contraction of the mass, 

 and the disappearance of a considerable quantity of vis viva; but as the 

 gases are bad conductors, and exist in a state of great division, the 

 emission of heat and of light is very feeble, (nebulous type.) 



There comes a time when by the progress of condensation, and by the 

 cooling of the surface of the nebula, chemical forces come into action j 

 there are then produced the liquid and solid particles which distinguish 

 the exterior strata of the gaseous mass the photosphere. But as the 

 solid aud liquid particles are denser than the rest of the mass, they fall 

 toward the center of gravity. There they are volatilized anew, under 

 the influence of the high central temperature, and determine ascending 

 currents of gas, which are in their turn cooled and feed thus the photo- 

 sphere, which is more or less agitated, according to the intensity of the 

 currents. (Type, sun, star.) 



When the entire mass of a star becomes thickened to such a degree 



* E. Plautauiour, Ohservalion de V eclipse totale de soldi du 18 juillet I860, a Castellon de 

 la Plana; Guillemin, Le del. 

 tSee further details of these hypotheses Faje CompleS rendus, t. ix, 1865, p. 89-96. 



