392 
MESSES. DE LA EUE, STEW AST, AND LOEWY’S EESEAECIIES 
esteemed it superfluous to spend very great labour, inasmuch as we came to the con- 
clusion that the distances from the centre of the various groups, as recorded by Schwabe, 
were not sufficiently precise to warrant very great refinement in the mode of estimating 
the foreshortening. We have not therefore attempted to make use of Schwabe’s obser- 
vations for the purpose of determining whether there be any law regulating the beha- 
viour with regard to increase or diminution of the groups as they pass across the disk 
of the sun, such as we have elsewhere attempted to deduce from Carrington’s observa- 
tions, but we have confined ourselves to estimations of the spotted area of the whole 
visible disk. 
We ought also to add that, in preparing our fortnightly mean values, those for the 
days in which the sun’s disk was not observed, were obtained by interpolation, so that 
in Table Y. the differences between the fortnights of Schwabe’s series and simultaneous 
fortnights of Carrington’s and of the Kew series may be partly accounted for by the 
fact that the days of observations at Dessau were not the same as those in this country. 
In fine, the differences registered in the Table include the uncertainty occasioned by 
interpolation, as well as that occasioned by the method of observation. 
Description of Tables and Plate. 
27. In addition to fortnightly values we have given three-monthly values for every 
fortnight, each of the latter being the mean of the three fortnightly values which 
precede, and of the three which follow it. 
We have given these three-monthly means in addition to the fortnightly means, inas- 
much as our experience has led us to conclude that in the former while we get rid of 
fluctuations of extremely small period, we yet preserve the most striking peculiarities 
which characterize the progress of solar disturbance. 
These three-monthly means form the curve in black which accompanies this paper. 
The dotted curve is obtained from the black by a simple process of equalization ana- 
logous to that described by the Astronomer Royal (Phil. Trans. 1863, p. 619), that is 
to say, the middle points of the various inclined black lines were joined together forming 
a curve of a smooth character, which by a repetition of the same process gave us the 
dotted line which indicates the larger or so-called eleven-yearly period of solar disturbance. 
In Table VII. we have the various fortnightly means forming the first column for 
each year, and the three-monthly means forming the second column. For convenience’ 
sake, in the margin of this Table each month is supposed to be capable of division, without 
much error, into four weeks ending on the 7th, the 14th, the 21st, and the 28th days of 
the month. The single fortnightly values are assumed to correspond in epoch to the 
7th and 21st days, while the three-monthly values on the other hand correspond to the 
14th and 28th. All those fortnightly values inclosed in brackets without an asterisk 
are interpolated. Those inclosed in brackets, and having an asterisk, are derived from 
Schwabe’s observations ; they occur during the time when Carrington had left off and 
before the Kew series had regularly commenced, and also during the time when the Kew 
