METHODS OF FORECASTING THE WEATHER. 163 



and the same type of atmospheric pressure distribution. W'ith the 

 increase of our knowledge on these points the weather predictions 

 will also become more and more accurate. However, it is verA'^ doubt- 

 ful whether it will ever be possible for us to invariably attain absolute 

 accuracy even for one day in advance. Ever}' increase in the percent- 

 a.ge of veritications is, however, of the greatest value, especialh' to 

 national economics. 



Now, as a matter of course, the meteorologists are looking every- 

 where in order to take ad^'antage of everything which may be of assist- 

 ance to them in this matter. In the first place, there are the man^^ 

 good weather rules that have been deduced from the experience of 

 many hundreds of years. But the greatest numljer and most valuable 

 of these weather rules are only applicable to local weather predictions, 

 whereas the central meteorological institutes must make their predic- 

 tions for verj' distant countries also, as, for example, Austria for 

 Dalmatia, Vorarlberg, Bukowina, etc. 



Those weather rules, however, which relate to the weather condi- 

 tions of certain definite dates, and which are generalh- looked upon as 

 farmers' rules, are sometimes of great assistance in making forecasts. 

 Thus we know that on certain dates of the yeav there has for centu- 

 ries been a tendency to a certain kind of weather; for example, to 

 -rainy weather. Therefore, if at such periods the distribution of 

 atmospheric pressure is of such a form that it may easily change to a 

 type corresponding to the weather indicated l^y the farmers' rules, 

 then we may be tolerably certain that we must forecast wet weather. 

 But, on the other hand, if at some such period the distribution of 

 pressure is of such a character as would ordinarily justify us in hoping 

 for a change of weather, still we know that this change is not likel}' 

 to occur, because there is a continued tendency at this period to wet 

 weather, and a change of weather is not to be looked for. Such aid as 

 this from farmers' rules is, however, of moderate value and rarely 

 available. But it is quite otherwise, in the opinion of the l)elievers in 

 the moon, when we consider the support that the weather predictions 

 might derive from hypotheses that attribute to the moon and the rest 

 of the heavenly bodies a decided influence on the weather. I will 

 express myself more in detail on this subject. 



First and foremost, I must insist most strongly on the fact that pro- 

 fessional meteorologists themselves have always recognized and do 

 recognize one influence of one heavenly body as most decisive and the 

 sole cause of the weather on our earth, viz, the heating of the earth 

 and of its atmosphere by the smi. The sun regulates our weather; it 

 gives rise to winter and summer; In* evaporation it raises the aqueous 

 vapor into the air, and this vapor, by cooling, produces clouds and 

 rain, snow, storms, and hail; it is the primary cause of the differences 

 in atmospheric pressure, and in this way produces the winds. 



