158 



an interpretation of the existence of a number of these 

 cloudy strata floating in the comet's atmosphere in con- 

 centric rings around its central mass in the presence of 

 atmospheric ingredients of diflferent chemical constitu- 

 tion, or in supplies of vapour furnished from the same 

 source at different intervals of time as indicated in the 

 alternate violent action and total cessation of the steamy 

 jets which have been observed to take place. But whilst 

 all this is going on upon the anterior or sunward side 

 of the comet, there is quite another state of affairs on the 

 opposite side. There the planetary mass and its cloudy 

 canopies project their shadows and their shades into a 

 vast conoidal space beyond, a space in which total and 

 partial eclipses of the sun prevail, where the influence of 

 the solar rays is felt with mitigated force, and where, con- 

 sequently, a misty precipitation is formed, which becomes 

 illuminated in the penumbra by the direct rays of the par- 

 tially eclipsed sun, and throughout its whole extent by 

 the scattered beams which penetrate the bank of filmy 

 clouds floating over the central planetary mass, and stretch- 

 ing away in a direction from the sun, forms that illumi- 

 nated appendage known as the cometary tail. 



It will be perceived, however, that though condensation 

 would be commenced, where the temperature was sufficiently 

 mitigated, throughout the whole of that coniodal space, 

 darkened by the intervention of the planet and its clouds, 

 yet, when once commenced, the inner particles of cloud 

 being largely protected from further radiation by those 

 external to them, the sum total of condensation would be 

 almost confined to an annular space near the circumference 

 of the shadow, in short, the misty cloud would have the 



