396 POPULAR LECTURES AND ADDRESSES. 



turbed by mountains, according to observations 

 made in balloons by the late Mr. Welsh, of Kew, 

 through a large range of heights. This diminu- 

 tion of temperature upwards in our terrestrial 

 atmosphere is most important and suggestive in 

 respect to the constitution of the solar atmosphere, 

 and not merely of the atmosphere or outer shell 

 of the sun, but of the whole interior fluid mass 

 with which it is continuous. The two cases have 

 so much in common, that there is in each case loss 

 of heat from the outer parts of the atmosphere 

 by radiation into space, and that in consequence 

 circulating currents are produced through the 

 continuous fluid, by which a thorough mixing up 

 and down is constantly performed. In the case 

 of the terrestrial atmosphere the lowest parts 

 receive, by contact, heat from the solid earth, 

 warmed daily by the sun's radiation. On the 

 average of night and day, as the air does not 

 become warmer on the whole, it must radiate out 

 into space as much heat as all that it gets, both 

 from the earth by contact, and by radiation of 

 heat from the earth, and by intercepted radiation 





