SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 425 



My own and Hann's views as to the part played by aqueous vapor 

 in meteorological processes differ from each other, as I believe, much 

 less than they appear to do. I also, for partly well recognized reasons, 

 attribute no special importance to i^recisely the same results of my com- 

 putation that Hann opposes. On this point allow me to make the fol- 

 lowing remarks : My computations "On the Esimnsion of the Air of the 

 Atmosphere in the Formation of Clouds," as I first published them eleven 

 years ago [" On Vertical Currents of Air in the Atmosphere," SchlomilcL, 

 Zeitschrift fiir Mathematik und Physik, 1864, Bd. 9, pp. 250-276; also, 

 Eeye, "Wirbelstilrme," Hannover, 1872], had for their immediate object 

 the overthrow of Mohr's theory of the formation of hail. Mohr main- 

 tained that because saturated steam has a much greater volume than 

 the water from which it is formed, therefore by the condensation of the 

 vapor at any point in the atmosphere there must be formed an " immense" 

 diminution of volume; this "formation of a vacuum" is, however, fol- 

 lowed by a strong indraft, an inrush of air, especially from the upper 

 strata, which then, by reason of their own cold, cause a new condensa- 

 tion, etc. In opposing this theory, it was sufficient for me to assume 

 that the air in which this condensation occurs loses no heat during the 

 process. ^^ 



With the same assumption, at the end of the chapter, I compute, inci- 

 dentally, the quantity of air that will be pushed out of a vertical column 



that in no instance, not even those of longer duration (and there occnr many of twelve 

 hours and over), did a sensible influence of the rain make itself apparent. The phe- 

 nomena are here precisely the same as Sykes gives for the Dekkhau (see Zeitschrift, x, 

 p. 12). There are, indeed, no data at hand relative to the extent of these rains, but we 

 know that at the rainy season, for instance in January, there are on the average of 

 seven stations in the Sunda Islands 21.3 days, and there must be a truly wonderful 

 arrangement if it does not occasionally rain simultaneously over nearly the whole Archi- 

 pelago, the more so since the rains occur very nearly at the same time of day. And 

 yet there is no disturbance of the diurnal period of the barometer! And what rains 

 were those compared with ours ! On the 10th January, 1867, there fell in one hour at 

 Batavia 97 millimeters, that is to say, only 3 millimeters less than falls with us in three 

 months, from December to February, when we have the lowest barometric pressure. 

 In this case, no minimum occurred, even at a great distance, that one could quote as au 

 excuse for any decided diminution of pressure. 



The facts quoted by Espy, Thom, and Loomis prove nothing against my assumption, 

 because the influence of the rain can only become prominent in the case of rainfalls 

 without an accompanying rotatory motion of the air, but where there is no wiiirl 

 there is also no notable barometric minimum. On this is founded the inductive por- 

 tion of my reasoning. On the other hand, I will readily allow that small diflerences of 

 jpressure (I have expressly said " no notable influence ") can, perhaps, be brought in 

 agreement with the results of the observations in Bat avia ; the land and eea breezes of 

 the tropics show that quite unnoticed barometric differences can bring about very 

 active currents of air. Such slight differences of pressure as these are quite sufiScient 

 to cause the continued flow of air toward that place in the whirl where condensation 

 takes place, and to explain its continuance and the direction of its progressive move- 

 ment, as I have already indicated on pages 292 and 344, vol. ix [see page 13, $ B, and 

 page 39, $ D, of the preceding translations of Hann's articles]. — J. Hann. 



10 Then, however, no condensation could occur ; therefore, also, no evolution of heat 

 and no exi^ansion ; and all further consequences likewise fall to the ground. — J. Hann. 



