. Bulletin of the Geological Society of America. Geology. o O 3: r—1 0 O fe O 33 0 r-> -V 32 IO Of) J -a a C-5 a V y-, 0 iH X t- tH O CO GO rH Ed 3 0) © T) 00 00 TJ » a 03 S> ft f-5 O 0 id Q X O a, ,a 1—1 'O c g cS tw 00 rH SQ CO 05 > *H PI 3 -a d CO >*) a a 00 oS 1—1 g 0 H e or a O CI 0 C 00 to c rH •iH 7: "3 1 02 Pi O rH CO 1 00 0 XII a 92 « & d O O CO rH O fa O cS 2 a b O 32 2 r^ rH 0 O 02 no .a i- eS 0 0 0> rH pi D CO rH iA © Then in succeeding cycles the maxima become moire and more p/ronounced until, in 1778, the number was , or nearly twice as much as in 175
. Bulletin of the Geological Society of America. Geology. o O 3: r—1 0 O fe O 33 0 r-> -V 32 IO Of) J -a a C-5 a V y-, 0 iH X t- tH O CO GO rH Ed 3 0) © T) 00 00 TJ » a 03 S> ft f-5 O 0 id Q X O a, ,a 1—1 'O c g cS tw 00 rH SQ CO 05 > *H PI 3 -a d CO >*) a a 00 oS 1—1 g 0 H e or a O CI 0 C 00 to c rH •iH 7: "3 1 02 Pi O rH CO 1 00 0 XII a 92 « & d O O CO rH O fa O cS 2 a b O 32 2 r^ rH 0 O 02 no .a i- eS 0 0 0> rH pi D CO rH iA © Then in succeeding cycles the maxima become moire and more p/ronounced until, in 1778, the number was , or nearly twice as much as in 1750. Thereafter there is a decline to only in 1816. An increase again fol- lows, and from 1837 to 1870 we have four maxima, all of which are above 95. Then the number of spots falls off once more. If we look at the dotted line joining the minima we see that it rises and falls in the same way as the line joining the maxima, although not nearly as much. In 1810 there were no sun-spots. An equally inactive state of the sun was not again attained until 1913. The low state of both the max- ima and minima at these two dates in- dicates a cycle whose length is some- where near a century. The interval from one main maximum to the next happens in this case to be somewhat different from the interval between the chief minima. The first great maxi- mum comes in 1778. Then comes an- other period of maxima with two main crests, one in 1837 and one in 1870. In figure 18 two heavy lines have been drawn at a height of 95 in order to bring out the periods of many sun-spots as compared with the periods of few. It is remarkable that not only does the height of the maxima vary at different periods, but the length of the individual cycles varies in the same way. Appar- ently at the end of a period of abundant solar activity the active force, whatever it may have been, becomes dormant and we have a long interval before an- other and much smaller maximum ap- pears. For instance, the int
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
