INTRODUCTION. 



XV 



for it is known that the air, at great elevations, contains more cal- 

 oric to the pound, than the air near the surface of the earth, be- 

 cause it is the upper regions that receive the caloric of elasticity, 

 given out in the condensation of vapor into clouds. Therefore, 

 when the air has descended some time in the middle, between two 

 ascending columns, the barometer will fall a little, or at least not 

 stand so high above the mean as it does on the outside of the two 

 clouds, and so the columns will be pressed towards each other. 

 If one of two neighboring columns should be greatly higher than 

 the other, as 3 and 2, (p. xii.) its annulus may overlap the smaller 

 one, and, of course, the current under the smaller cloud will be in- 

 verted, and the cloud which may have been formed over the col- 

 umn thus forced to descend will soon disappear ; for as it is forced 

 downwards by the overlapping annulus of the more lofty column, 

 it will come under greater pressure, and its temperature will be 

 thus increased ; and it is manifest, that as soon as its top descends 

 as low as its base, it will have entirely disappeared ; and, in the 

 mean time, the larger cloud will have greatly increased. 



As the air above the cloud formed by an ascending column is 



57. For an account of the manner in which one spout, while forming, tends 

 to generate others in its neighborhood, see page 435. 



