90 S P. Langley—Minute structure of the Solar Photosphere. 
shape. They have just been spoken of as relatively definite 
in outline, but this outline is commonly found to be irregular 
tain tendency to foliate structure which is characteristic of 
them, and which has not been sufficiently remarked upon. 
This irregularity and diversity of outline have been already 
observed by Mr. Huggins. Estimates of the mean size of 
less conjectural. Mr. Dunkin, using about four inches aper- 
ture, found between two and three hundred of them in a space 
56” by 48”. If we call the number two hundred and fifty, 
we have their average distance apart about 3-4’ (= 28%), 
which is certainly too great. In the almost total absence of 
micrometric determinations, the following, though imperfect, will 
have interest. With the Rogers micrometer and near the cen- 
ter of the sun, with a power of 240 and an aperture of 9 inches, 
18 rice-grains were counted in one square (11/6 on the side). 
In the next square there were 15, in the next 23. These differ- 
ences are not so much due to imperfect estimation as to a re 
irregularity of distribution. On another occasion, witha higher 
wer, 15 rice-grains were counted in a line whose length was 
8’'87 and on an adjacent part of the disc, in the same length, 
12. From the mean number in these squares and the value of 
the side of a square in arc, we deduce 2’”57 as the distance 
between the centers, while with the higher powers we obtain 
a value of but 1-42, with every increase of telescopic power 
the number of minute bodies counted as rice-grains thus being 
* It is well to remember that even upon this estimate each of these “minute” 
