umber of days of observation,
and further the days when the sun was free from spots. The number of
groups alone will not in itself give sufficient accuracy for determination
of a period, since I have convinced myself that when there are a large
number of sun-spots the number will be reckoned somewhat too small, and
when few sun-spots, the number somewhat too large; in the first case
several groups are often counted together in one, and in the second it is
easy to divide a group made up of two component parts into two separate
groups. This must be my excuse for repeating the early catalogue, as
follows:--

+---------------------------------------------+
| Year.| Number of | Days free | Days of |
| | Groups. | from Spots.| Observation.|
|---------------------------------------------|
| 1826 | 118 | 22 | 277 |
| 1827 | 161 | 2 | 273 |
| 1828 | 225 | 0 | 282 |
| 1829 | 199 | 0 | 244 |
| 1830 | 190 | 1 | 217 |
|---------------------------------------------|
| 1831 | 149 | 3 | 239 |
| 1832 | 84 | 49 | 270 |
| 1833 | 33 | 139 | 267 |
| 1834 | 51 | 120 | 273 |
| 1835 | 173 | 18 | 244 |
|---------------------------------------------|
| 1836 | 272 | 0 | 200 |
| 1837 | 333 | 0 | 168 |
| 1838 | 282 | 0 | 202 |
| 1839 | 162 | 0 | 205 |
| 1840 | 152 | 3 | 263 |
|---------------------------------------------|
| 1841 | 102 | 15 | 283 |
| 1842 | 68 | 64 | 307 |
| 1843 | 34 | 149 | 324 |
|(1844)| (52) | (111) | (320) |
+---------------------------------------------+

"If we now compare together the number of groups, and the days free from
spots, we find that the sun-spots have a period of about ten years, and
that for about five years they are so numerous that during this period few
days, if any, are free from spots. The sequel must show whether this
period is constant, whether the minimum activity of the sun in producing
spots lasts for one or two years, and whether this activity increases more
quickly than it decreases."

[Illustration:

FEB