424 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



until at last it rests upon tbe earth and begins to rain. These signs are 

 recognizable at a distance of 200 or 300 nautical miles from the hurri- 

 cane." 



These accordant results of extended systems of meteorological obser- 

 vations in America, Europe, and the South Indian Ocean, especially the 

 important fact that the harometric minimum advances toward the side of the 

 heavier precipitation, plainly show the appreciable influence of the con- 

 densation of the atmospheric aqueous vapor upon the change of atmos- 

 pheric pressure. Furthermore, the known laws connecting the tension 

 and temperature of aqueous vapor and of the atmosphere force us to 

 assume some such direct influence. Local observations like those at 

 Batavia can, in my opinion, not prove the contrary, since they leave us 

 entirely in ignorance as to the extension of the rainfall and as to the 

 simultaneous meteorological phenomena of the surrounding portion of 

 the globe. The enormous rainfall of 2d and 3d December, 1872, which 

 overflowed the whole of Carinthia,Carnatia, Gorz, Northern Venetia, and 

 Southern Tyrol, has shown in what distant regions many times we must 

 seek the prime cause of very heavy and extended rains. "^ Certainly at 

 that time no one on the south flank of the Alps suspected that this rain 

 was caused by a barometric minimum on the coast of France^ and even 

 to-day it would be inexplicable to us why that enormous precipitation 

 did not at least cause a secondary minimum,^ unless we had an accurate 

 knowledge of the configuration and the atmospheric conditions of half 

 of Europe. 



So far as concerns the 146 heavy rainfalls at Batavia, these appear, 

 so far as concerns their duration and geographical extension, to have 

 had the characters of local thunder-storms ; for among them those of 

 more than three hours' duration were so infrequent that Hann could not 

 give any average for the fourth hour of rain. Now, in the case of local 

 storms, even when they are accompanied by heavy precipitation, the 

 accompanying rarefaction can very rapidly be restored, because the 

 region of condensation occupies a relatively very small space in an im- 

 mense atmosphere. Moreover, the process of condensation, i. e., the 

 formation of the storm-clouds, begins at least in our latitudes, generally 

 a considerable time before the outbreak of the storm ; and if during the 

 subsequent rain the pressure rises a little by reason of the cooling of 

 the lowest stratum of air, I therein find nothing contradictory to the 

 theory. ^ 



" Compare this, Zeitschrift, vol. viii, pp. 103, 179. 



* If a sensible barometric depression could be caused by rain, then certainly here 

 at least a secondary minimum must have been formed ! — J. Haxx. 



*To this I remark in brief only as follows, but in general refer to jiages 11 and 12 of 

 this present volume x [see the preceding translation (C) of Hann's reply to HoiJ- 

 meyer's remarks]. — J. Hann. 



In reference to the rains at Batavia, I have submitted the heavier short rains to com- 

 putation, because these must best represent the effect of an ascending current of air, 

 and because an examination of the whole series of observations showed me at once 



