1875.] Variation of the Sun's Heat. 33 



What proportion the variation may hear to the total incident heat, the 

 present data of course cannot show ; and in order to know this, we must 

 await the regular actinometric observations which it is to be hoped may he 

 undertaken at the new Solar Observatory under Col. Tennant at Simla. 

 But judging" from the present results, it would certainly appear probable 

 that the variation is such as must exercise a very appreciable influence on 

 the Meteorology of our earth. " It is a dynamical law absolutely universal 

 and one which extends beyond the domain of mere dynamics, that all 

 periodicity in the action of a cause, propagates itself into every, even the 

 remotest effect of that cause, through whatever chain of intermediate arrange- 

 ments the action is carried out."* 



If then the sun's radiation vary directly with the number of the spots 

 and prominences, every other meteorological phenomenon must likewise so 

 vary, rainfall and temperature included, and we have therefore a priori 

 grounds for the validity of Meldrum, Lockyer, and Koppen's discoveries. 

 With regard to the rainfall, the coincidence of its variation with that of the 

 sun spots has been only partially verified by the data ; but seeing that the 

 rainfall of the larger part of the world has not been taken into considera- 

 tion in the comparison, this is no more than we should expect. In India, 

 for instance, the registers of most of the few stations that have been com- 

 pared, fail to conform to the supposed law, but India is but a small part of 

 the region on which precipitation takes place during the SW. monsoon, and 

 I have shewn in a former volume of this Journal, that there are independent 

 grounds for believing, that owing to protracted variations in the distribution 

 of atmospheric pressure in different years, (from what causes arising we are 

 at present unable to determine,) deficient rainfall in one part of the monsoon 

 area is probably compensated in great part by an excessive rainfall elsewhere. 

 As far as the coincidence has been established, the quantity of rain that falls, 

 varies directly with the intensity of the sun's radiation ; in other words, with 

 the quantity of energy received from the sun, which of course determines the 

 quantity of water evaporated and afterwards condensed. 



This consideration appears to me to throw some light on the apparent- 

 ly anomalous variation of temperature detected by Professor Koppen.f 

 He finds that, in the tropics, the maximum temperature coincides, not with 

 the maximum of the sun-spots, but more nearly with their minimum ; which, 

 however, it precedes by \ to 1-| years. His inference, partly based on this 

 fact, and partly on his erroneous idea of the nature of the spots, is the 

 reverse of that which follows from the facts now adduced. He concludes 

 that the spots are an indication of the diminished radiation of the sun, 



* Herschel's 'Meteorology,' p. 137. 



f Zeitsch. d. Oesterr. Gresellschaft fur Meteorologie, Vol. VIII, pp. 2il and 257. 

 5 



