December 6, 19C0] 



NA TURE 



i\\. 



The Hainfall at the Cape, Batavia attd Cordoba for 

 the Period 1 877-1 886. 



Each of the curves illustrating the rainfall for the Cape 

 and Cordoba for this period shows two prominent maxima 

 in the years 1878 and 1883 ; these correspond nearly 

 with the + and - pulses of solar temperature. Com- 

 paring them also with the Bombay and Mauritius curves 

 for the same period, it is found that the pulses indicated 

 at Bombay occur simultaneously with those of 1878 and 

 1883, but in the case of Mauritius the effect of each of 

 the pulses is felt about a year or so earlier, namely 1877 

 and 1882 (Fig. i). 



The rainfall curve for Batavia for this period has its 

 most prominent maximum in the year 1882, like that of 

 Mauritius, thus preceding by a year the pulse felt at the 

 Cape, Cordoba and Bombay in 1883. 



The Time Conditions of the Pulses. 

 The various curves which we have drawn for the pur- 

 poses of study have been compiled from yearly means. 



generally to be the case. Thus after the mean solar tem- 

 perature of 1876, the - pulse was felt first at Mauritius, 

 then in India and the Cape. After the mean of 188 1, the 

 4- pulse was felt first at Mauritius, then in India and the 

 Cape. Cordoba felt both pulses in the same year as 

 India and the Cape. 



Subsidiary Pulses. 



In a normal sun-spot curve we find a sharp rise, 

 generally taking three or three and a half years, to 

 maximum, and a slow decline to minimum, on which the 

 remaining years of the cycle are spent. 



The curve on the upward side rises generally regularly 

 and continuously ; on the downward portion the regu- 

 larity of the curve is very often broken by a '• hump " or 

 sudden change of curvature. There has not yet been a 

 complete discussion of the number and character of the 

 prominences associated with the spots during the cycle ; 

 we have found, however, that the "hump" in the sun- 

 spot curve in 1874 was accompanied by a remarkable 

 increase in the number of eruptive prominences. 



1880 MADRAS. 

 " N.W.P. 



I866- 9.N.W.P. 1868 LOW NILE 



1860- 1 N.W.P. 1858-9 " " 



1837- 8 U.IND IA. 



1824 MADRAS. 



1884-5 BENQAL 

 MADRAS 



I87S-4N.WR 1873 LOW NILE. 

 75 -6 BOMBAY. 

 76-7B0MBAr !8''7 ■• " 

 " U.INDIA. 

 •• MADRAS. 



1865-6 MADR.\S. 

 0RIS3A. 



Fig. 2. 



1890 N.W.P. 

 1891 -2 MADRAS. 



" BOMBAY. 



" BENGAL. 

 1632 N.W.P. 



and, so far, in these curves the rainfall in months has not 

 been considered. That will have to come later. Hence if 

 the rainfall which most influences the yearly mean occurs 

 in the last three months at one place, and in the first three 

 months of the next year at another, they are shown as 

 being a year apart, whereas they have actually been con- 

 tinuous. 



With regard to the travel of the pulses over large areas 

 under the influence of the S.E. trade, it may be gathered 

 from the pressure charts that the -I- and — conditions of 

 pressure are apt to lie over the centres of land and water 

 areas, and not generally over coast lines. In the case of 

 water surfaces, the effect of a sudden change in the solar 

 radiation on the pressure might be expected to be felt not 

 at the point where the pressure is least or greatest at the 

 time, and of the most general type, but where the equili- 

 brium is most unstable. On the other hand, more time 

 would be required for the new pulse to establish itself 

 where the conditions are more complicated. 



Hence we should expect the pulses to be felt first in 

 the eastern part of the southern ocean, and this seems 



NO. 1623. VO L. 63] 



We have already referred, in discussing the Indian 

 rainfall, to a remarkable intensification of the south-west 

 monsoon in 1874-5, the effect of which is especially 

 noticeable in the rainfall of the Konkan and North- West 

 Provinces, and we have come to the conclusion that we 

 must consider all these events as due to a common cause, 

 that is, to a subsidiary solar pulse. We propose to return 

 to this subject in a subsequent communication, after 

 inquiries have been completed relating to 1885-6 and 

 1896-7. 



The Intervals betzveen the Pulses. 



There will obviously be intervals between the ending 

 of one pulse and the beginning of the next, unless they 

 either overlap or become continuous. 



The + and — pulses, to which our attention has been 

 chiefly directed, are limited in duration ; and when they 

 cease the quantity of rain which falls in the Indian area 

 is not sufficient without water storage for the purposes of 

 agriculture ; they are followed, therefore, by droughts, and 

 at times subsequently by famines. 



Taking" the period 1887-89 we have (Fig. 2) 



