288 



REPORT 1864. 



§ 6. Variation- of the Hygrojietric Condition of the Air with Elevation. 



All the adopted readings of the temperature of the dew-point in. Section 4 

 were laid down on diagrams, and joined bylines drawn from one to the other. 

 In the case of the temperature of the air, when thus joined, a curved line can 

 be di-awn through them, giving equal weight to every observation, but tliis 

 cannot be done with respect to the temperature of the dew-point, it being far 

 more variable than the temperature of the air, and the numbers in the fol- 

 lowing Table are those as read at every 1000 feet from the diagram formed 

 simply by joining the point of observation. 



Table VII. — Showing the Variation of the Hygrometric condition of the 

 Air at every 1000 feet of Height. 



Fourteenth Ascent. 



August 31. — The temperature of the dew-point on the ground before 

 starting was 56°-7, or 7°-3 below that of the aii- ; at 1100 feet these two 

 temperatures were both 54°, the air being satui-ated with moisture ; at 1150 

 feet the air suddenly became drier, the difference between the temperatures 

 of the air and dew-point was 5° ; at 7100 feet the temperatures of the air 

 and dew-point were 34° and 18° respectively, and remained at these values 

 nearly, while the balloon ascended to more than 8000 feet and descended to 

 7900 feet. The difference between the temperatures of the air and dew-point 

 after this was generally less and less to 3000 feet, at which clouds were 

 entered, and the air was nearly saturated with moisture ; at 1000 feet high 

 the temperature of the air was 49°, and that of the dew-point 47°'4. 



The balloon then reascended, and on again entering cloud at 1580 feet, the 

 air was again saturated with moisture, and on descending, it was nearly satu- 

 rated at 1200 feet and at 820 feet ; at the latter height the respective tempe- 

 ratures were 53° and 52°. 



