68 PROCEEDINGS OF THE AMERICAN ACADEMY 



cause of tlie general depression of the chromosphere, on account of 

 the imperfect data, it seems natural, however, to suppose that the 

 phenomenon is connected in some way with the minimum period of 

 sun spots. Judging by the great number of veiled spots observed, 

 and by the myriads of pores seen between the granulations, it would 

 seem that both the chromosphere and photosphere have been much 

 thinner than nsual during the present year. 



If there are breaks in the photosphere at many points of the sur- 

 face of the sun, it becomes easy to account for the unusual thinness of 

 the chromosphere this year, because, as observed by myself and others, 

 at certain phases of the spots, the chromospheric gases, rushing with 

 impetuosity into the umbra, go down under the photosphere like gigan- 

 tic waterfalls, diminishing consequently the thickness of the chromo- 

 sphere. That this takes place I shall give amjile proof in another 

 communication. 



It seems evident that the chromosphere near a spot is kept off from 

 falling into the opening by a force from the interior. As soon as this 

 force decreases in energy, immediately the chromosphere tends to 

 cover it, and even to precipitate itself through the opening when this 

 force becomes extinct. The observations show this plainly. 



Wlien a spot is decreasing, it is quite common to observe that the 

 umbra and penumbra appear as if they were seen through a heavy 

 fall of snow, their surfaces being covered by numerous bright flocculent 

 granulations surrounded by a kind of bluish fog. In a few instants of 

 very rare definition, I have been surprised to see faint traces of this floc- 

 culent appearance upon almost all the spots ; indeed it would seem that 

 the spots -are rarely free from some faint traces of the chromospheric 

 gases. Probably the bright flocculent objects observed upon the umbra 

 and penumbra of spots, are the granulations of the chromosphere dis- 

 solved to a greater or less degree by the forces emanating from the spots. 



Perhaps it may not be idle to remark that, during the period men- 

 tioned, I have almost every day observed small groups of facuhc in the 

 polar regions, especially near the north pole of the sun ; while, for the 

 most part, they have been entirely absent from the equatorial regions, 

 where they are commonly found. 



To conclude, my observations show : — 



l'^. That during this year, and especially during the interval from 

 June 10 to August 18, and to a less degree to September 

 14, the chromosphere has been notably thinner than usual 

 upon the entire surface of the sun. 



