Sept 26, 1878] 



NATURE 



567 



Which of the two methods, then, is [the more applicable to 

 t!ie data for discnssion ? 



Of all the methods, that of the harmonic analysis is doubtless 

 the best. It enables us to see whether there is any parallelism, 

 and if there is a cycle, what is its probable length with respect 

 to the sun-spot cycle, the range of variation, the times of 

 maximum and minimum, with their intervals, &c. I have 

 applied this method to yearly values of the rainfalls, and of the 

 levels of rivers of various countries, and have come to the con- 

 clusion that, notwithstanding all apparent irregularities, there is 

 an intimate connection between sun-spots and rainfall. 



If the rainfall generally was above its mean in the years of 

 maximum sun-spot, and below it in the years of minimum sun- 

 spot, we should get for the mean yearly rainfall of a number of 



stations the equation "~ — 



where S is the mean 



^ - S r' -K 

 value of the sun-spots for the period examined, s the mean value 

 of the spots when below S, s' their mean value when above S, 

 and J?, r, r' the corresponding values for the rain for the years 

 from which S, s, and s' were obtained. This formula applied to 



the public observations of different countries shows that with very 

 few exceptions the rainfall for the periods examined were above 

 the average. The results for the mean rainfall of fifty-fcur 

 stations in Great Britain, and thirty-four in America from 1824 

 to 1867 are as follows : — j 



Great Britain 



America 



= -8356 

 = "8333 

 = -8356 

 = -8407 



In other words, the rainfall of fifty-four stations in Britain 

 from 1824 to 1867 was 075 inch below the mean when the sun- 

 spots were below their mean and 0*90 inch above it when the 

 spots were in excess, and the corresponding values for America 

 were 0*94 and 1"I3 inch, C. Meldrum 



Sun-spots and Weather 



In Nature, vol. xvii. p. 326, Dr. Balfour Stewart concludes 

 an article with the following remark : — 



"It is nearly, if not absolutely, impossible from observations 

 already made, to tell whether the sun be hotter or colder as a 

 whole when there are most spots on his surface. The sooner 

 we get to know this the better for our problem." 



Tlie Bombay barometric observations appear to me to afford 

 fairly conclusive evidence in favour of the sun being hottest about 

 the time of maximum spotted area, and coldest when the spotted 

 area is at its minimum. 



It is well known that in Central Asia the annual variation of 

 the barometric pressure is greater than in any other portion of 

 the globe, and it is universally admitted that this variation is due 

 to the great variation of tempcratiu-e between summer and 



winter, the barometer being low when the temperature is high, 

 and vice versd. If, therefore, the absolute heat of the sun is 

 subject to considerable variations, we ought to find the baro- 

 metric pressure in Central Asia responding to those variations 

 just as it does to the annual variations of temperature ; in other 

 words, the summer barometric minimum should be lowest in 

 those years when the sun is hottest, and the winter maximum 

 should be highest in those years when the sun is coldest. 



Similar results should be obtainable from the barometric 

 records of any station where the annual variation of pressure is 

 considerable and of the same character as in Central Asia. 

 Bombay is such a station, and one where cyclonic disturbances 

 are less frequent and violent than at most other Indian coast 

 stations. I give below the mean barometric pressure at Bombay 

 for the summer and winter half-years from 1847 to 1877 : — 



The winter means correspond in time to the beginning of each 

 year, the summer means to the middle of each year. Taking 

 the mean of each pair of winter means, we obtain a new set 

 of numbers which correspond to the middle of each year, and 

 which give a somewhat smoother curve than the original num- 

 bers, and performing a similar operation twice upon the summer 



means, we obtain a "similarly .smoothed set of numbers also 

 corresponding to the middle of each year. These two sets of 

 smoothed numbers, and their means, are given below, and 

 graphically represented by the accompanying curves, along with 

 the inverted sun-spot curve. 



