195 
remark that in the latter case the variation is simply periodic 
and the number of revolutions of the phase therefore twice as 
small as in the ease of the moon’s revolution. 15 we assume 
therefore, that, in calculating the twenty-six-day period, the 
error committed is twice as large and suppose the error to 
he inversely proportional to the number of observations taken 
into account, we find as an estimate of the error committed: 
0.0027 x 1440 х э = 0.00548, 
7740 
The value 25.8120 having been deduced not only from baro- 
metrie daily means, but from several independent series, we 
may safely assume that, in determining this quantity an ac- 
curacy of + 0.005 days is secured. As to the epoch it is at 
once evident from the formulae that an error in the quantity š 
leads to a corresponding error in the determination of the epoch 
twice as large when the variation is double- as when it is simple- 
periodic, consequently the errors of the values found for the 
epochs will hardly exceed 10 degrees i. e. less than one day. 
7. This conclusion bears necessarily a somewhat arbitrary 
character, but in any case it Is evident that the mean period 
of duration of the variation deduced from meteorological data 
is considerably smaller than that calculated from magnetical 
data, which is about 23.86 days, for it is sufficiently proved 
by the results of this inquiry thal an error of 0.05 days is out 
of the question. On the contrary, ifan error has been committed 
at all, it certainly is on the side of the value 25.86 in consequence 
of the inadequate method by which it has been deduced. 
It is of some importance however to remark that, as far as 
up to the present our knowledge of the sun’s constitution goes, 
it is not peremptorily necessary that the value, deduced from 
Magnetical data, be identical with that calculated from mete- 
orological observations. It is highly probable that the different 
layers of the sun are moving with different angular velocities , 
the smaller the farther the distance from the centre, an assump- 
