100 S&S P. Langley—Minute structure of the Solar Photosphere. 
It is very desirable to determine whether the penumbral 
slope is forme a superior (or lateral) pressure which 
separates the photosphere, or whether it is built up by the 
deposits of vapors ascending from the sides of the umbra. I 
have made (B,;, B,;) a careful transcript from nature of eve 
granule or filament visible in the penumbral edge for this dis- 
tance. T'o me it seems that the edge of a torn piece of cloth, 
with its projecting threads, would not give clearer evidence of 
rupture. 
I cannot conclude this description without speaking of the 
umbre, though their study would form a chapter by itself 
The polarizing eye-piece gives us interesting information about 
the nuclei or those darkish shades of the umbra discovered by 
awes. 
Are these round, nearly central openings, so that looking 
into one we are looking into the axis of the cyclone to which 
the spot is due,—into the vortex of the great whirl down which 
the chromospheric vapors are being sucked by mechanical ac- 
tion? Are they ragged apertures—the craters as it were of 
eruptions whence metallic vapors are being forced up? The 
answer to this question, were there but these two alternatives, 
would be definitive as to our choice between the principal 
theories of solar circulation. But we cannot answer peremp- 
r 
could not present their usual aspect with the downward suc- 
tion of a cyclone beneath them. 
I will briefly recapitulate those of the results of these tele- 
scopic studies which seem to have been before little observed 
or undescribed. 
The ultimate visible constituents of the solar photosphere 
being, not the rice-grains, but smaller bodies which compose 
them, and the size of these latter being valuable at not over 
0’3; from a comparison of the total area covered by them 
with that of the whole sun, we are entitled to say that the 
greater part of the solar light comes from an area of not over 
one-fifth of its visible surface, and which may be indefinitely 
We must then greatly increase our received estimates of the i- 
tensity of the action to which solar light (and presumptively us 
heat and actinism) are due, on whatever theory we form them. 
(There is a presumption from observation that there is a drift 
of all the photosphere in a direction approximately parallel to 
