SUN-SPOT, STORM, AND FAMINE. 35 



the total emission of light and heat at the times of maximum 

 and minimum has been measured, without any assumption of 

 the kind, we cannot decide the question. 



More satisfactory would seem to be the measurements 

 which have been made by Professor Piazzi Smyth, at 

 Edinburgh, and later by the Astronomer Royal at Green- 

 wich, into the underground temperature of the earth. By 

 examining the temperature deep down below the surface, all 

 local and temporary causes of change are eliminated, and 

 causes external to the earth can alone be regarded as 

 effective in producing systematic changes. "The effect 

 is very slight," I wrote a few years ago, "indeed barely 

 recognizable. I have before me as I write Professor Smyth's 

 sheet of the quarterly temperatures from 1837 to 1869 at 

 depths of 3, 6, 12, and 24 French feet Of course the most 

 remarkable feature, even at the depth of 24 feet, is the 

 alternate rise and fall with the seasons. But it is seen that, 

 while the range of rise and fall remains very nearly constant, 

 the crests and troughs of the waves lie at varying levels." 

 After describing in the essay above referred to, which appears 

 in my " Science Byways," the actual configuration of the 

 curves of temperature both for seasons and for years, and 

 the chart in which the sun-spot waves and the temperature 

 waves are brought into comparison, I was obliged to admit 

 that the alleged association between the sun-spot period and 

 the changes of underground temperature did not seem to 

 me very clearly made out It appears, however, there is a 

 slight increase of temperature at the time when the sun-spots 

 are least numerous. 



That the earth's magnetism is affected by the sun's 

 condition with respect to spots, seems to have been more 

 clearly made out, though it must be noted that the 

 Astronomer Royal considers the Greenwich magnetic ob- 

 servations inconsistent with this theory. It seems to have 

 been rendered at least extremely probable that the daily 

 oscillation of the rnagnetic needle is greater when spots are 

 numerous than when there are few spots or none. Magnetic 



