72 Dr. Herschel on the Nature , &c. 
elastic fluid; as is evident from its not instantly filling up the 
cavities of the spots, and of the unevenness of the mottled 
parts. It exists, therefore, in the manner of lucid clouds 
swimming in the transparent atmosphere of the sun ; or ra- 
ther, of luminous decompositions taking place within that at- 
mosphere. 
