INFLUENCE OF ALTITUDE ON PRECIPITATION. 127 



all Btatioiis furnish data, according to the author, represeut two extreme and two 

 average years, and are therefore quite useful. 



The very large mass of material permitted a sifting out of doubtful observations 

 without impairing the number of available ones for the construction of a raiu map 

 of Bohemia, showing by isohyetal lines seven rain-belts or zones; the zones are 

 arranged so that the lowest shows less than 500 mm. rainfall, the three following 

 difler by 100 mm. each, the fifth and sixth by 200 mm., and the seventh by 300 mm. ; 

 the last showing, therefore, a rainfall of 1,200 to 1,.500 mm. 



The central basin divides itself into two halves by a line from north to south, 

 running somewhat east of the middle Moldau, crossing the Elbe near the mouth of 

 the Iser. and following the latter river; the western half showing the smaller amount 

 of precipitati<m, namely, 500 to 600 mm. ; the eastern with 600 to 700 mm., continuing 

 in a small belt along the foot of the Erzgebirge and the Boehmerwald encircling the 



first zone. 



The other isohyetal lines do not embrace continuous areas, but follow in small 

 belts the trend of the mountains. The largest amounts of precipitation are found in 

 belts or islands in the higher altitudes of the mountains which surround this great 

 basin. The continuity of the zones is much interrupted, so that it would be difficult 

 to describe them without a map. 



The maximum of rainfall, with over 1,200 mm., is observed in the south, near the 

 sources of the Moldau and Motawa; in the north, near the sources of the Elbe, Iser, 

 and Aupa. on the range of the Schneekoppe. In regard to the distribution through 

 the months, the experience has been confirmed that with increasing absolute height 

 the winter precipitation increases in greater proportion than the summer precipita- 

 tion, while those of spring and autumn are nearly equal. 



SuflScient material was on hand from which to calculate the influence of altitude 

 on the increase of precipitations, although for altitudes above .500 m. the material 

 is not considered sufficiently reliable. Yet the general law is well shown that with 

 the altitude the quantities of precipitation increase in a retarded progression. 

 This progression is calculated by forming altitude zones from 100 to 1000 m., group- 

 ing the stations in each, calculating the mean elevation and also the mean annual 

 precipitation as observed for each class; then by dividing the difference of precipi- 

 tation in the neighboring two zones by the difference of altitude the amount of 

 precipitation which corresponds to each 1 m. elevation within that class is found. 

 With this figure the average amount of rainfall which theoretically belongs to each 

 station according to its absolute elevation can be approximated by adding to or sub- 

 tracting from the mean precipitations of the class as many times this amount as the 

 actual altitude diff'ers from the meau. 



An example will make this clear : Tetschen, for instance, is situated 150 m. above 

 sea level. According to the table the average elevation of thirteen stations of the 

 lowest zone, to which Tetschen belongs, is 182 m., with an average precipitation of 

 506 mm. Now, Tetschen has an elevation 32 m. lower than the average; its normal 

 rainfall should therefore be 32 X 0.79 = 25.4 mm. less than the mean of the class; 

 hence, theoretically, according to its altitude, the quantity of rainfall for Tetschen 

 should be 506 — 25.4 = 480 mm. ; that is 248 mm. less than that actually found in an 

 eight years' average. By using the figures for the two extreme zones and dividing 

 by 100 the mean increase of precipitation for every 100 m. elevation is found to be 



69 mm. 



And now comes the application of this method to our proposition. The author 

 argues that if thp actually observed rainfall differs considerably from the theoret- 

 ically determined, this is ^,^ indication tbat special agencies are at work. He finds 

 pow that of the pne hundred a^d eighty-six stations which he subjects to scrutiny 

 (these offering the Jongest »pd mpst trustworthy observation), forty-eight show a 

 considerable difference between thp observed and the theoretically expected rain- 

 fall, and he finds also that these §t)a|;ipps ^^-e ^ituatpd iu the most densely wpode^ 

 portions of ^hp Kingdom. 



