THE SUN-SPOT PERIOD. 147 



face would be —78° C/' if the solar radiation did not exist. Now, the 

 actual mean temperature of the earth is about +15° C.,'' from which it 

 follows that the effect of solar radiation is to raise the mean teniDer- 

 ature of the earth 88° C. above the temperature of space. 



The mean area covered b}" sun spots during a ^ear of maximum 

 activity may l)e taken as not far from one one-hundredth of the total 

 area of the sun's disk. From this it follows that the radiation is 

 diminished b}' the presence of sun spots by about one two-hundredth, 

 and this should produce a diminution of terrestrial temperature of 

 about jVt)° or 0°.MC. 



This, it will be remembered, is almost exactly the result obtained 

 above from the discussion of direct observations as representing- the 

 excess of mean terrestrial temperature during the 3'ears of minimimi 

 over those of maximum sun spot activity.'" 



«[Note by translator.] Professor Poynting gives the temperature of space at 

 —263° C. 8ee Phil. Trans, of the Royal Society of London, Series A, vol. 202, p. 

 529, 1903. 



&Hann: Klimatologie. Stuttgart, 1897. 



cl desire to express here my thanks to M. Mascart, who has been so good as to 

 place at my disposal for this investigation the library of the Bureau Central meteo- 

 rologique, and to M. Angot, who has given me most valuable counsel. 



[Note by translator.] The author's discussion of temperature departures in 

 connection with the sun-spot cycle has aroused considerable interest among meteor- 

 ologists. It is fair to say that while expert opinion is not entirely in accord with 

 him in his methods of study and conclusions, the criticism which has been called 

 forth by his paper seems to indicate that meteorologists require further evidence 

 rather than that they wholly disbelieve in the alleged association of sun spots and 

 temperatures. 



Professor Angot, in an article translated for the Monthl}- "Weather Review of Au- 

 gust, 1903 (p. 371), strongly objects to Nordmann's procedure of smoothing the yearly 

 temperature departures and combining observations from numerous stations, on the 

 gi'ounds of uncertainty of the real mean temperatures of some stations, and of the 

 prejudicial effect upon the general mean of unequal lengths of the series of observa- 

 tions at the several stations. He prefers to treat each station separately, and gives 

 reductions of data from Guadaloupe, Hongkong, Batavia, Bombay, Barbados, and 

 Habana, extending over periods ranging from ten to fifty years, and embracing 16 sun- 

 spot periods altogether. Fourteen of these periods yield results in the same general 

 direction as those obtained by Nordmann, and 2 in the contrary, so that Professor 

 Angot remarks that "the probability is, then, according to these observations, 7 to 1, 

 that an increase in the number of sun spots is accompanied by a diminution in the 

 temperature." It appears from his reductions that "an increase of 100 in AVolf's 

 relative sun-spot numbers (a difference which frequently exists between a maximum 

 and a minimum) will be accompanied by a diminution of 0°.33 C. in the value of the 

 mean annual temperature." Professor Angot concludes: "It is evident that in order 

 to determine the value [of the temperature departure for an increase of 100 sun-spot 

 numbers] it would be necessary to work with a much larger lunnber of series. I have 

 given the numbers which j)recede only as an example of a method which appears to 

 me more exact and more convincing than that ordinarily employed." 



Professor Abbe, commenting editorially on the articles of Nordmann and Angot 

 (Monthly AVeather Review, October and December, 1903), refers to a discussion of 



