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between minimum and maximum become shorter at the time of 
greater solar activity (highest ordinates of the spot-curve, 1.e. greates. 
Total Spotted Area), and conversely. It is W. Lockyer’s merit to 
have pointed out the importance of the former quantity J/—m for 
several phenomena that may have some connection with the solar 
activity. 
A. — In figure 1 the abscissae represent the years, the ordinates 
the values of M—m. So for instance the ordinate 5.0 for the year 
1884.0 represents, according to Lockyrr, the interval between the 
minimum of 1879.0 and the maximum of 1884.0. A similar ‘mini- 
mum to maximum curve” is given by Lockyer for the period 1834— 
1890, in a figure agreeing with our diagram. L. prolongs his curve, 
beginning from 1900, by a dotted line, in the expectation that in 
conformity with the course of the curve between 1867 and 1870 *) 
the fluctuation will rise to a maximum soon after 1901. The real 
course, however, of the solar activity since the time (1900) at which 
L. established his period, is contrary to his expectation. [now make 
use of Wotrer’s results based on all the principal series of solar 
observations *). It. needs no demonstration that the results of these very 
carefully compared observations — lately 22 series obtained at places all 
over the earth have been included — furnish the best, or rather the 
only reliable basis for discussion and cannot be superseded by any 
single series of observation, such as that of the Solar Physics Obser- 
vatory. For the rest Worrer’s results agree in the main with those 
obtained independently in another way and from different materials 
by Gumtaume in Lyons*), by Mascarr and Riccò at Catania *) and 
by Epstein at Frankfurt on the Main °). 
Now the mean values of Worrrr for the years since 1867, lead 
to the following values of the intervals of time Mm in the four 
last sunspot-cycles : 
1) Lockyer’s diagrams in Knowledge and Scientific News Voi Il. Jan. p. 35, 
and Fe p. 7, 1905, may be consulted: the predictions quoted above are still more 
clearly set forth in these passages. 
2) A. Worrer, Astron. Mitteilungen XCII (V. J. S. Naturf. Gesells. Zürich XLVI, 
1902) tables If and IV and diagram. 
5) J. Guittaume, successive volumes of the Comptes-Rendus de |’Ac. d. Sciences, 
Paris. 
4; A. Mascari, afterwards A. Riccò, Memorie della Societa degli spettroscopisti 
Italiani, successive years. 
5) Tu. Epstein, V. J. S. Astron. Gesellschaft 1880—86, and Astr. Nachrichten 
4237 (1908). For Epsrern’s important and too little noticed ‘Intensivzahlen” see 
especially: Die Sonnenflecken, Frankfurt a. M., Gebr. Fey. 1904, p. 139. 
v 
