SUNSPOTS AND WEATHER. 5°7 



as rainfall or barometric pressure, which it has been customary to 

 record. We find periods of a day and a year, but the differences of the 

 averages from the actual observations are very considerable. 



The next step consists in trying to find out whether cycles can be 

 discovered in these differences, and for this purpose the same method is 

 followed. But the periods to be examined are by no means obvious. 

 The time of revolution of the moon, under the supposition that the 

 moon has any influence, is not found in meteorological observations, 

 or at any rate the effect is so small as to be negligible in comparison 

 with what we want to find, and no other astronomical period seems 

 very likely to find a counterpart in the records. There is, however, 

 one period which at first sight appears to be a possible one in meteoro- 

 logical observations, namely, that known as the sunspot period. Be- 

 fore going into the evidence for its existence as a climate factor, it is 

 necessary to say a word or two about the effects of periodic changes. 



These changes may be roughly divided into two classes, those of 

 short period and those of long period. From the former we should 

 expect changes from day to day or every few days, constituting what 

 we usually call the i weather.' Nothing at all is known of the exist- 

 ence of any such period, all attempts to trace one having ended in 

 absolute failure. The long period changes are in general those which 

 affect the character of a season and which show the difference between 

 one season and the next, or the variations which a given season of the 

 year will show in several successive years. In countries where the 

 most important interests are manufacturing and ocean transportation, 

 the ' weather ' is the first consideration ; in lands where the agricultural 

 interests are predominant, although the weather is important, it is more 

 essential to have an idea of the climatic or seasonal changes. Thus 

 if the sunspot period could be shown to have a large influence on the 

 climate of any region, we should be able to forecast to a corresponding 

 extent the general characteristics of future seasons, and lay plans ac- 

 cordingly. The practical value of such an investigation is obvious, but 

 its scientific interest is not less if it leads to a more accurate knowledge 

 of the laws of nature. The case therefore deserves examination. 



In order to establish any connection between sunspots and 

 meteorological changes, two things are necessary. First, the periods 

 in which the sunspots can be grouped must be discovered and their 

 relative importance determined. Second, the meteorological records 

 over long intervals of time must be examined in order to see whether 

 they exhibit similar cycles of change and whether those cycles, sup- 

 posing that they exist, are sufficiently well-marked to be considered 

 important factors in the variations of the seasons at any place from 

 year to year. 



Although the existence of sunspots has probably been known from 



