Jan., 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



reference will now be made, the deduction is that great 

 heat variations do occur. 



If the sun's disc be scanned from time to time, it will 

 be found that sometimes there are spots and some- 

 times there are none (fig. i). According to our 

 present knowledge these spots are produced by the 

 descent of comparatively cool matter from the higher 

 reaches of the solar atmosphere, so that the more spots 



18/6 1877 1878 'l879 



Fig 



^e dark portion shows the variation in the £ 

 1 the Sun from year to year for an eleven = i 

 three prominent outbursts in the year* 1870 and 1871 



there are, the greater the quantity of matter descending. 

 Since this falling material is the result of previous up- 

 rushes of highly heated matter from the lower levels of 

 the sun's atmosphere, it stands to reason that this spot 

 phenomenon indicates great solar atmospheric disturb- 

 ance and therefore greater activity and consequently 

 more intense heating capacity. Thus we arrive at the 

 conclusion that the greater the number of spots, the 

 greater the solar activity and therefore the hotter the sun. 

 Now there is a decided periodicity in spot activity. 

 For some years only a few spots become visible, while 

 a little later they become more numerous until a maxi- 

 mum is reached, after which they begin to dwindle again 

 in numbers until the succeeding minimum is attained 

 when the sun remains spotless for months together. The 

 accompanying diagram (fig. 2) will give the reader a 

 good idea of this variation. The dark portion, which 

 looks like a silhouette of a cathedral city, shows the 

 change of the amount of "spottedness " of the sun for 

 each solar rotation from the year 1867 to 1879 ; the arrows 

 indicate the "epochs" or times, as determined from a 

 curve specially smoothed for this purpose, when there are 

 fewest (minimum) or most (maximum) spots. It will be 

 noticed that there is not a gradual mcrease of spotted area, 



SCALE OF YEARS 

 I 2 3 4 5 6 7 8 9 10 II IZ 13 

 ■ ' ' ' ' ' I ' ' ' ' ' ' ' 



18340 

 1943-5 

 18560 

 1867-2 

 1879- 

 IBa9-6 

 1901 •;? 



1 I I I I I I I t I I t I ■ 



Fig. 3. — The lengths of the period from minimum to minimum 

 change alternately. 



but that, as the diagram shows, there seem to be intermittent 

 outbursts. From this figure, which includes a whole 

 sunspot cycle, it will be seen that the time from one 

 minimum to the next is about twelve years; this, how- 

 ever, is not always the case. A glance at the next dia- 

 gram (fig. 3) shows that since 1834 the lengths of these 

 periods are alternately longer and shorter than the pre- 

 ceding one, the mean length being a little more tiian 

 eleven years. It will thus be seen that the 

 so-called " eleven year cycle " of sunspots is only 

 approximately true. A reference again to figure 

 2 shows further that the epoch of maxinmm 

 occurs nearer the preceding than the following 

 minimum ; this is always the case, only from 

 one period to another this interval from mini- 

 mum to maximum is not the same. To illustrate 

 this, these intervals are arranged in figure 4 

 one below the other, and instead of an alter 

 nate change in length they recur every third 

 period. Thus if this apparent law holds good the 

 approaching maximum will occur about a little 

 more than three years after the last minimum 

 (this occurred in about the middle of 1901), that is 

 about the end of the present year (1904). Another curious 

 fact relating to the sun-spot cycle is that when the interval 

 from minimum to maximum is shortest, the total amount 

 of "spottedness" included in the whole period from 

 minimum to minimum is greatest. This is graphically 

 shown in the accompanying diagram [fig. 5). The last 



1834 



1843-5 

 «856 



1667 



i 



I I I I I I I 



pi„ 4. -Diagram to show that the interval between a minimum and 

 the following maximum changes in a cycle of about 35 years. 



square represents the relative spotted area that may be 

 expected for the present cycle if the previous conditions 

 be repeated. . . 



The above brief summary of the sun-spot variations 

 tells us that not only does the heat of the sun change, 

 but that these changes occur in cycles of about eleven and 

 thirty-five years. There is, further, another cycle, not 

 very well indicated, which has a period of less than eleven 

 years, probably the same as that which is more clearly 

 defined by the solar prominence ob;ervations to which 

 reference will now be made. 



The solar activity can also be gauged from "pro- 

 minence " records. These disturbances are probably of 

 more consequence than those of spots. The latter are 

 strictly limited as regards position on the sun's surface 



