SUNSPOTS AND VOLCANIC AND SEISMIC PHENOMENA. 71 



humid. Then in the torrid zone the earth is screened by a 

 canopy of vapour ; the otherwise excessive temperature is 

 lowered also by the voluminal (adiabatic) expansion of the 

 atmosphere, and also by great evaporation. Hence the 

 summer may be sultry, but evaporation, condensation, 

 cloudiness and adiabatic expansion reduce the actual 

 temperature as recorded by the thermometer. The winter 

 would for the same reason also be mild. In years of sunspot 

 minimum, however, the tropics would in summer be less 

 protected by vapour, and the compression of the whole 

 atmospheric shell would also raise its temperature. In 

 temperate regions, however, the effect of a sunspot maxi- 

 mum would be to raise temperature somewhat in winter, 

 the wet season, and to make the summer drier and subject 

 to intensely hot days. A sunspot minimum would however 

 be accompanied in the temperate regions by cool summers 

 and excessively cold frosty winters. It will be seen that 

 with these explanations, the results obtained by Nordmann, 

 Koppen, Hann aud McDowall are not inconsistent, and 

 agree well. 



III. Sunspots and Barometric Pressure. — Regarding 

 sunspots and barometric pressure it seems to be quite 

 certain that there is a connection. Meidrum has shown 

 for the West Indies and Mauritius that more cyclones pass 

 in years of maximum sunspot effect than in minimum years. 

 This probably involves a diminution of pressure. Blanford 

 has shown for the India area that the mean yearly pressure 

 undergoes variations which correspond to the inverted 

 sunspot curve, being highest at sunspot minimum. The 

 later researches of Dr. Lockyer, Professor Bigelow and 

 others, show that the earth is divisible into two areas 

 over which the pressure variations are reciprocal. 1 Dr. 



1 " Monthly Weather Review," Vol. xxx., No. 7, p. 347, and Roy. Soc. 

 Proc, Vol. lxx., p. 500, and Vol. lxxi. 



