610 
NATURE 
[APRIL 28, 1904 
and (3) a very narrow, dark line running through the 
centre of H, and K, designated H, and K,. 
Now according as the second slit is made to isolate 
any part of either of these lines, so a calcium 
picture of the sun corresponding to this particular part 
of the line is obtained. 
It may perhaps be 
* flocculi ”’ 
mentioned that the name 
is here employed to designate the clouds 
of vapour which are photographed with the spectro- | 
heliograph. When the calcium line is employed 
“calcium flocculi’’ are photographed, or if the 
hydrogen line be used we obtain ‘‘ hydrogen flocculi.”’ 
These flocculi are, according to Prof. Hale, situated 
at a greater level above the photosphere than the 
“faculz,’’ the latter being elevated regions of the 
photosphere. 
As the width of the H and K bands depends on the 
density of the calcium vapour, and the denser calcium 
in the sun is below that of less density, the pictures 
of the sun secured by using different parts of these 
lines will correspond to different levels. In fact, a 
means is thus employed of photographing sections of 
the calcium vapour, or of sounding the solar atmo- 
sphere with respect to this element. Thus, if the second 
H 
Fic. 2.—Reproduction of a photograph showing the H and K lines ot 
calcium in the solar spectrum when large dispersion is employed, 
slit be set at the extreme edge of H, or K,, the result- 
ing photograph will only show that calcium vapour 
which is dense enough to produce a line of this breadth, 
in fact, a section across the base of the calcium 
flocculus will be obtained. If set nearer the centre 
of the line a section of the flocculus corresponding to 
a higher level will be produced. 
Further, this calcium picture in the final positive is 
always bright on a dark background no matter which 
parts of the H or K lines are employed. That this is 
so can be seen from Prof. Hale’s pictures taken in the 
H, or H,, or K, or K, light; this is an important point 
to which reference will be made later. 
An examination of several photographs has led Hale 
to deduce that the calcium flocculi when secured with 
the slit nearer H, or H,, or K, or K, are more exten- 
sive than those taken near the outer edge of H, or K,. 
It is argued from this that the calcium flocculi are 
most probably in general composed of a series of 
columns of vapour expanding as higher levels are 
reached, and possibly overhanging laterally (Fig. 3). 
To explain this point a little more fully perhaps the 
accompanying diagram (Fig. 4) may prove of service. 
In the centre of the diagram is drawn (on rather an 
exaggerated scale) the H line of calcium, and below 
NO. 1800, VOL. 69] 
this are lettered the detailed portions of it according to 
Hale’s nomenclature. Above this are drawn three 
layers to represent three strata of calcium vapour 
corresponding to the width of the H line, which varies 
according to the density of the vapour. To investigate 
the distribution of the densest layer the portion H, of 
the H line is used, H, is employed for the less dense 
layer, and H, for the least dense. 
Fic. 3.—Showing that the bright calcium flocculi are more ex- 
tensive at the Hy level (upper photograph) than at the Hy 
level (lower photograph). Notice that the spot is nearly 
obliterated at the Hg level. 
At the right-hand side of Fig. 4 is a sketch of a 
portion of the solar surface taken separately with H,, 
H,, and H, lines, and we have therefore the H,, H,, 
and H, flocculi. As, according to Hale, the area of 
the H, flocculus is more extensive than that of H,, 
and H, more extensive than that of H,, if we project 
this to gain a mental image of the vertical distribu- 
tion of this calcium vapour we obtain an object some- 
what after that drawn above the three calcium flocculi. 
