on 
dissociation take place Where this occurs, 
spots are replaced by a gentle rain of fine particles slowly de- 
scending, insteal of the fall of mighty masses and large 
quantities of solid and liquid material. 
Volatilisation will take place gradually during the 
and at the utmost only a veiled spot will be produced. 
We know that when the solar forces are weak, such a descent is 
taking place all over the sun, because at that time the spectrum 
of the corona, instead of being chiefly that of hydrogen, is one 
of a most complex nature—so complex that before £882 it was 
regarded by everybody as a pure continuous spectrum, such as is 
given by the limelighr. 
Th2 moment the fall of spot material begins we get the return 
current in the shape of active metallic prominences, and the pro- 
duction of cones and horns which probably represent the highest 
states of incandescence over large areas and extending to great 
heights ; and, besides these, the production of streamers (see 
Fig. 4). 
descent, 
Two results follow :— 
(1) In consequence of the increased temperature of the lower | 
rezions, the velocity of the lower carrents towards the poles, 
andtherefore of the upper currents from the poles, is enor- 
Fic. 3.—Minimun. 
NATORE 
[| uly 15, 1886 
mously increased. 
increased. 
(2) Violent uprushes of the heated photospheric gases, mount- 
ing with an initial velocity of a million miles an hour, can al<o 
disturb the ring directly. 
In this way the sudden rise to maximum in the sunspot curve, 
and the lowering of the latitude of the spots, follow as a matter 
f course. And the pirt of the ring nearest the sun, its base, 
so to speak, is, it would appear, thrown out of all shape, and 
we get falls over broad belts of latitude N. and S. 
Does this hypothesis explain, then, the slow descent to mini- 
mum and the still decreasing latitude? It does more, it 
emands it. For now the atmosphere over those regions where 
the spots have hitherto been formed is so highly heated and 
s height is so increased, that any disturbed material descend- 
1g through it will be volatilised before it can reach the photo- 
yhere. 
The best chance that descending particles have now to form 
pots is if they fall from points in lower latitudes. The final 
ae 
The disturbance of the rinz will therefore be 
it 
II 
y; 
period, therefore, of the sunspot curve must be restricted to a 
very large extent to latitudes very near the equator, and this is 
1e fact also, as is well known. 
Mguator 
Tracing of the results obtained by the cameras in 1873, showing inner portion of equatorial extension, and how the surfaces of it cut 
the concentric atmosphere in lat. 35° N. and S., or thereabouts. 
: It will be seen that on this view, as the brightness, and there- 
fore the temperature, of the atm sphere, as we know, increases 
very considerably from minimum to maximum, the masses which 
can survive this temperature must fall from gradually increasing 
heights. 
It may be pointed out how perfectly this hypothesis explains 
the chemical facts observed and associates them with those 
gathered in other fields of inquiry. 
At the minimum the ring is nearest the sun, the subjacent 
atmosphere is low and relatively cool. 3 
Particles falling from the ring, therefore, although they fall in 
smaller quantity because the disturbance is small, have the best 
chance of reaching the photosphere in the same condition as 
they leave the ring, hence at this time the widening in many 
familiar lines of iron, nickel, titanium, &c. i 
The gradual disappearance of these lines from the period of 
minimum to that of maximum is simply and sufficiently explained 
by the view that the spot-forming materials fall through gradu- 
ally increasing depths of an atmosphere which at the same time 
is having its temperature as gradually increased by the result of 
the action I have before indicated, until finally, when the maxi- 
mum is reached, if we assume dissociation to take place at a 
| higher level at the maximum, dissociation will take place before 
is very gradual. 
| conditions at the maximum to be maintained for some time 
the vapours reach the photosphere, and the lines which we know 
in our laboratories will cease to be visible. 
This is exactly what takes place, and this result can be con- 
nected, as I have stated elsewhere, with another of a different 
kind. This hypothetical increasing height of fall demanded by 
the chemistry of the spots is accompanied by a known accelera- 
tion of spot movement over the sun’s disk, as we lower the 
latitude—which can only be explained, so far as I can see, by a 
gradually increasing height of fall as the equator is approached. 
There are two other points. (1) The sunspot curve teaches 
us that the slowing down of the solar activities at the maximum 
We should expect, therefore, the chemical 
afterwards. As a matter of fact, they have been maintained 
till March of the present year, and only now is a change taking 
place which shows us chemically that we are leaving the maxi- 
mum conditions behind. (2) The disappearance of the lines of 
the metallic elements at maximum is so intimately connected | 
with an enormous increase in the indications of the presence of 
| 
| 
