NO. 4 TEMPERATURE NARIATIOXS IX THE NORTH ATLANTIC 163 



radiation toward the earth's surface would be 30 times as much 

 diminished as the outgoing- radiation from the earth. In Hum- 

 phrey's opinion the eleven-year variations may be produced because 

 the sunlight according to his view has less violet and ultra-violet 

 rays at sun spot maximum than at minimum, on account of the 

 presence in the solar corona at maximum of the maximum number 

 of particles which reflect and scatter the light. Since the ultra- 

 violet rays form ozone, conditions will be more favorable to its 

 formation in the isothermal layer of our atmosphere above 11 

 kilometers altitude during sun spot minimum. But since the ozone 

 has the peculiarity of transmitting the visible heat rays relatively 

 freely but of hindering the escape of the long wave length rays 

 emitted by the earth, the increased formation of ozone will be ac- 

 companied by a rise of temperature at the earth's surface because 

 the outgoing radiation of the earth is diminished. \\'e shall later 

 return to the consideration of Humphrey's theories. 



A valuable article was published by Dr. Johannes ^lielke (1913) 

 in which he discussed the yearly temperatures from 1869 to 1910, 

 for not less than 487 diiTerent stations distributed over the whole 

 earth. He has divided these stations into 25 regions, the same which 

 Koppen had used before, and thereby has found means to determine 

 the most probable expressions for the temperature of the different 

 parts of the earth's surface during the investigated period. These 

 temperature series show on the whole an unmistakable agreement 

 with the variations in the number of sun spots, but this agreement 

 is most marked for the tropics. As the average amplitude between 

 the warmest years at sun spot minimum and the coldest years, at 

 sun spot maximum, he finds for the tropics in the years 1820 to 

 1854: 0.65° C. ; in the years 1870 to 1910 : 0.40° C. Outside the 

 tropics in the years 1820 to 1854: 0.51° C. ; and the years 1870 to 

 1910: 0.35° C. 



In the following year (1914) Koppen published a new investiga- 

 tion on the temperature of the earth, the sun spots, and the vol- 

 canic eruptions which was based principally on the two above men- 

 tioned articles of !\Iielke and Humphreys. He employed the values 

 for the temperature series used by Mielke in order to construct 

 curves which bring out clearly the agreement between the variations 

 of the temperature of the earth's atmosphere and the sun spots (see 

 fig. 65 below). The best agreement is found as already stated in 

 the tropical variations. Koppen discussed Humphrey's theory that 

 the temperature variations depend in part upon the volcanic erup- 



