448 NATURE [Marcu 10, 1904 
the curves drawn as shown in the figure previously re- | maximum spot-activity were joined up with each other, 
ferred to. year by year, for the period of time over which the curves 
In this way it was possible to trace the varying positions, 
as regards changes of latitude, of the centres of action, or 
maxima points of the curves, from year to year, just as 
was previously attempted in the case of the prominences. 
These centres of action were then connected by lines pass- 
ing from one yearly curve to the next. It is worthy of 
1860-0 1870-0 1880:0 
00 
SUNSPOTS 
MEAN DAILY 00 
AREA 
N.HEM®& 400 
° 
Latitupes or °° 
CENTRES OF 60 
ACTION 
or 40 
PROMINENCES 
é 20 
N. HEME 
° 
MEAN 
HELIOGRAPHIC #9 
LATITUDE oF to 
SUNSPOTS 
N. HEMS ° 
30 
LATITUDES OF 
CENTRES OF 
ACTION 3 
oF 
SUNSPOTS 
N.HEM® 
LATITUDES OF 
CENTRES OF ° 
ACTION 70) 
oF 
SUNSPOTS : 
Ss. HEMS 30 
MEAN ° 
HELIOGRAPHIC 
LATITUDE OF 
SUNSPOTS 20 
S.HEMs, 
° 
LATITUDES OF = 29 
CENTRES OF 
ACTION 40 
oF 
10 
PROMINENCES 8° 
5S HEMS, i-{o} 
200 
SUNSPOTS 
MEAN oAlLy 20° 
AREA 
400 
S. HEME 
° 
1860-0 
1870-0 1880-0 
Fic. 2.—A comparison of the curves illustrating (A) spot-activity tracks ; (B) mean heliographic latitude 
(c) prominence-activity tracks ; (b) variation of spotted area. (The continuous and 
broken vertical! lines indicate the epochs of sun-spot maxima and minima respectively, the two 
of sun-spots ; 
hemispheres being taken together.) 
remark that very little difficulty was met with in deciding 
the maxima points to be joined. There was always, 
throughout the whole period, a most distinct march of these 
points individually towards the equator, and the method 
of placing the curves one beneath the other rendered such 
movement at once obvious to the eye. 
The diagram (Fig. 1) not only exhibits some of the types 
of curves met with, but shows how the various centres of 
NO. 1793, VOL. 69] 
1890-0 
extend, namely, from 1879, the year following a sun-spot 
minimum, to about a sun-spot maximum in 1883. 
Considering the curves relating to the sun’s northern 
hemisphere, it will be seen that in 1879, the year following 
a sun-spot minimum, when the spots were ending a cycle 
near the equator, two new outbreaks occurred in latitudes 
about 20° and 30°. These two 
centres of activity moved towards 
the equator next year, and by 1881 
the former had disappeared, while 
the other rapidly grew in intensity 
and reached latitude 15°. During 
this year a new outbreak in latitude 
30° made its appearance, and this in 
the two following years had an 
equatorial trend. A somewhat 
similar occurrence took place in the 
southern hemisphere, each of the 
centres of action moving rapidly to- 
wards the equator. 
It is interesting to note the rapid 
growth and decay of these centres 
of action, an example of which is 
shown commencing in 1879 in lati- 
tude 28° in the northern hemisphere. 
Attention may particularly be 
directed to the three prominent 
maxima of the curves for the 
southern hemisphere in the years 
1882 and 1883, which indicate that 
at this period there were three de- 
finite centres of spot action in 
existence. 
To bring the results of the above 
analysis for the whole period of time 
investigated within a small compass 
the same method was adopted as 
that employed in the case of the 
prominence reduction to which re- 
ference has already been made. 
In Fig. 2 the two sets of curves 
marked A indicate for each hemi- 
sphere the changes in the positions 
of these centres of spot-activity from 
year to year, plotted at equal in- 
tervals of a year. The striped por- 
tion is deduced from  Sporer’s 
observations, and the remainder 
from the Greenwich reductions. 
‘These lines have been proportionally 
thickened to indicate approximately 
the relative amount of spotted area 
at these centres of action, or, in 
other words, the heights of the 
maxima points on the yearly curves. 
These curves thus indicate for each 
year the positions, as regards lati- 
tude, of the centres of spot activity, 
and give an idea of the movements 
of these centres during each sun-spot 
cycle. 
As these curves have here been 
called ‘‘ spot-activity tracks,’’ so 
““ prominence-activity tracks ’’ may 
be employed to indicate the equiva- 
lent variations as regards the 
prominences. 
For the sake of comparison, curves 
B, C, and D have been added. 
Curves B show the variations of the 
mean heliographic latitude of the 
total spotted area for each hemisphere. Curves C illustrate | 
the distribution and changes of position of the centres of 
prominence activity, or ‘* prominence-activity tracks ’’ as 
they may now be called. The small circles in the years 
1870-1871 represent Respighi’s observations, the curves 
from 1872-1881 those of Secchi and Tacchini, and the re- 
mainder, up to the year 1902, Ricco and Mascari’s observ- 
ations. The dotted curves previous to 1870 are intended 
1900-0 
