294 METEOROLOGY AND ALLIED SUBJECTS. 



opinion that at present exist relative to the use of the term ascending 

 current. Saussure first employed the term " courant ascendant^^'' which 

 Hann would restrict to the column of air ascending from mountains at 

 midday, and he doubts whether a similar general ascending current 

 ever developed itself over extensive horizontal areas of warm earth. 

 That many meteorologists have described the daily ascent of the lower 

 strata of air as going on continuously and not as a local interchange be- 

 tween ascending currents on the one side and descending on the other, is 

 evident to all, especially when we consider how many have fruitlessly 

 endeavored to explain the afternoon barometric minimum as the result 

 of the ascending current. 



Hann finds a strong argument against the invariable existence of an 

 afternoon ascending current in the fact that frequently at Vienna, as 

 elsewhere, absolutely cloudless afternoons occur, even when the dew- 

 point at the earth's surface is so high that an ascent of a few thousand 

 feet must produce cumulus clouds. The cumulus clouds that frequently 

 occur at very great altitudes are seldom due to currents ascending from 

 the immediate neighborhood of the observer, but to a rising and falling 

 or wave-like movement in the upper current itself. At these altitudes 

 the air is very near its dew-point, wherefore a very slight ascent would 

 give rise to formation of clouds. The direct interchange of air between 

 the upper and lower strata of the atmosphere seems not to extend to 

 very great altitudes in the atmosphere. {Z. 0. G. M., XIV, p. 352.) 



Kox)pen has published an extensive essay on boen, or wind gusts and . 

 thunder storms, which is reprinted with additions in the Journal of the 

 Austrian Meteorological Association. He concludes by inclining to the 

 belief that the gusts of wind preceding showers of rain are brought 

 down by the friction and resistance of the falling drops. In this view, 

 however, we believe that he was long since anticipated by Prof. Joseph 

 Henry. In regard to the gusts accompanying the b6en when no rain 

 falls, he thinks that this consists of air brought down from the upper 

 regions by its greater density, but still retaining the great horizontal 

 velocity that prevails aloft. 



The indications of the self-recording barometer show that every gust 

 of wind is accompanied by a corresponding disturbance of the barome- 

 tric pressure, and the table quoted by him furnishes many illustrations 

 of this. These disturbances are additional to those caused by the 

 action of the wind on the doors and chimneys of the room in which the 

 barometer is placed, and relate to the motion and density of the air in 

 the neighborhood of the observer. {Z. 0. G. M., XIV, pp. 457 to 478.) 



Sprung remarks that the law according to which bodies moving hori- 

 zontally are deviated to the right or to the left by the influence of the 

 rotation of the earth, notwithstanding its importance for meteorology, 

 appears to be still very little known. " In the course of my investiga- 

 tions it appeared clear to me that the reason why the theory of Hadley 

 and Dove as to the influence of the earth's rotation on the wind is at the 



