LABORS OF THE JOINT COMMITTEE. 167 



If these fluctuations depend on the increase and diminu- 

 tion of elasticity of the air by heat and cold, according to 

 a theory published in the Journal of the Franklin Institute, 

 the morning maximum of a considerable elevation ought to 

 be greater than on the plain below ; and the afternoon mini- 

 mum should not be as low as on the plain below. 



Again, the night maximum should be less and the mini- 

 mum greater than on the plain. These predictions have 

 been verified by observations. If time and opportunity 

 should be found, they might be repeated. 



The theory, however, goes further : it indicates that at 

 very great elevations there are but two fluctuations in a 

 day a maximum about twelve or one o'clock in the day, 

 and a minimum about day-break. To verify or refute this 

 inference from theory, simultaneous observations at an ele- 

 vation of fourteen or fifteen thousand feet, and on the plain 

 below, continued for a few days, will be sufficient, if the 

 fluctuations on the plain are regular. If a cloud is pro- 

 duced by the cold generated by the expansion of air as it 

 ascends, it is manifest that the base of the cloud will be 

 low in proportion as the dew point approaches near to the 

 temperature of the air, and high in proportion as the dew 

 point recedes from that temperature 



The Franklin Kite Club, at Philadelphia, have lately 

 discovered that in those days when columnar clouds form 

 rapidly and numerously, their kite was frequently carried 

 upwards nearly perpendicularly by columns of ascending 

 air, and they say in their report, that this circumstance be- 

 came so familiar during the course of their experiments, 

 that, on the approach of a columnar cloud just forming, they 

 could predict whether it would come near enough to affect 

 their kite ; for if the cloud did not pass directly over the 

 kite, the kite would only move sideways towards the cloud. 

 Now these upward columns were probably formed of air 

 heated from contact with the ground. 



