1845] WRITINGS OF JOSEPH HENRY. 227 



The change in the temperature during the intervals of 

 observation, is due to the variations in the temperature of 

 the room differently affecting the two extremities of the pile. 



In consequence of cloudy weather, another set of observa- 

 tions was not obtained until the 10th of January, and at 

 this time the spot had very much changed its appearance; 

 the penumbra, while it retained its dimensions in one direc- 

 tion, was much narrowed in the other, and the dark part 

 was separated into two small ones; also the sky was not per- 

 fectly clear and therefore the results were not as satisfactory 

 as those of the previous observations ; the indications were 

 however the same as in the other sets, exhibiting a less degree 

 of heat from the spots. 



Cloudy weather prevented other observations on the heat 

 of different parts of the sun, particularly a comparison be- 

 tween the temperature of the centre and the circumference 

 of the disc, which would have an important bearing on the 

 question of an atmosphere of the sun. The observations 

 will be continued, and any results of interest which may be 

 obtained, will be communicated to the Society, 



* At this observation a slight cloud probably passed over the sun's disc. 



