1875.] 21 



VI. — On some recent Evidence of the Variation of the Sun's Seat. — By 



Hekey F. Blanford, Meteorologist to the Government of India. 

 (Received June 1st ; — Read June 2nd, 1875.) 



Since the British Association meeting at Brighton in 1872, at which 

 Mr. Meldrum brought to notice the fact that the Cyclones of the Indian 

 ocean vary in frequency with the period of sun-spot frequency, several at- 

 tempts have been made to trace out the evidence of a similar periodicity in 

 other meteorological phenomena. Mr. Meldrum and Mr. Norman Lockyer 

 have done this in the case of the rainfall, with the result of shewing that in 

 the Mauritius, Australia, South Africa and some other parts of the world 

 such a variation is to be detected more or less distinctly in the registers. 

 And Professor Koppen has arrived at a similar conclusion in the case of 

 air temperature, a result on which I shall have again to offer some remarks 

 in the sequel. All these results point to the conclusion that the radiation 

 of the sun is not appreciably constant from year to year,* but varies with 

 the appearance and physical state of his surface. 



Long prior to any of these discoveries, the possible variation of the 

 sun's heat and of its influence on the earth had been the subject of specula- 

 tion among solar physicists. According to Professor Wolf, (as quoted by 

 Professor Koppen,) Riccioli, in 1651, shortly after the first discovery of sun- 

 spots, surmised that some coincidence might exist between them and terres- 

 trial weather changes. Sir William Herschell endeavoured to establish such 

 a connexion by discussing one of their remote effects, viz., the rise and fall 

 in the price of wheat in past years. Sabine established a connexion between 

 the solar-spot period and that of magnetic storms ; Fritz between the former 

 and the frequency of auroras ; and finally, in 1867, Mr. Joseph Baxendell of 

 Manchester succeeded in tracing out a distinct and very striking relation 

 between the number of the sun spots, and the ratio that exists between the 

 difference of the mean maximum temperature of solar radiation and the 

 mean maximum air temperature on the one hand, and that of the mean 

 temperatures of the air and of evaporation on the other. 



All these investigations, it will be noticed, have dealt with the problem 

 in an indirect form : that of Mr. Baxendell being, however, the most direct, 

 and perhaps as direct as the data at his command (six years observations 

 of the Badcliffe observatory, and five years of Mr. Mackereth's register at 

 Eccles near Manchester) would admit of. The causes that interfere with the 

 direct transmission of the sun's heat to the earth's surface are so powerful and 

 at the same time so variable, that even with more perfect instruments than 

 * As was assumed by Mr. Meech in his elaborate treatise on Solar heat in the 

 IXth Volume of the "Smithsonian Contributions to Knowledge." 



