170 REPORT— 1865. 



§ 5. Variation op Temperature op the Air ■with Height. 



Every reading of temperature in the preceding Tables, or the means of 

 small groups of readings when observations have been taken in quick succes- 

 sion at about the same altitude, or when the Balloon has passed and re- 

 passed through nearly the same space within a few minutes — as, for example, 

 on December 1st, between 3 h 44 m and 3 h 49 m it fell from 4464 feet to 3470 

 feet, and rose to 4170 feet — these readings, or means of readings, were laid 

 down on diagrams, the points joined, and a curved lino made to pass through 

 or near them, so that the area of the spaces between the original and tbe 

 adopted lines on one side Avas equal to that of the spaces on the other side. 

 Thus treated, temperature decreased with increase of elevation on December 

 1st and 30th. On February 27th it was found to increase, after attaining 

 the altitude of 4647 feet. On descending, the temperature at first declined, 

 and at 4800 feet the reading was the same as at the same elevation on as- 

 cending ; then a warm current was met with, and the readings at the same 

 elevation were much higher than were noted in ascending, and continued so 

 through a space of 2800 feet, below which they were lower than on ascend- 

 ing ; in consequence of these differences no temperature has been adopted for 

 these, and another ascent and descent were made, for which temperatures 

 have been adopted. 



The numbers in the first column show the height in feet, beginning at the 

 groimd and increasing upwards ; the numbers in the second column show the 

 interval of time in ascending to the highest point; the notes in the third column 

 show the circumstances of the observations ; the numbers in the fourth and 

 fifth columns the observed and the approximate normal temperatures of the 

 air ; and those in the next column the difference between the two preceding 

 columns, or the most probable effect of the presence of cloud or mist on the 

 temperature, or other local disturbing causes. 



The next group of columns is arranged similarly for the descent, and the 

 other groups for succeeding ascents and descents. 



