264 



REPORT — 1864. 



In every ascent a second thermometer has been used to check the accuracy 

 of the readings of the dry thermometer, and the truthfulness of the tempera- 

 tures shown by it ; in some of the ascents a delicate blackened bulb thermo- 

 meter was placed near to the place of the dry-bulb thermometer, fully ex- 

 posed to the sun in cloudless skies, or to the sky at all times : the readings of 

 this instrument were nearly identical with those of the di-y-bulb thermometer 

 in clouded states of the sky, and thus acted as an additional check. At all 

 times one or the other, or both Eegnault's and DanicU's hj^grometer, have been 

 used sufficiently often at all heights to show whether the wet-bulb thermo- 

 meter was in proper action, and to check the results given by the use of the 

 dry- and wet-bulb thermometers on the reduction of the observations. 



In all cases the readings of the dry-bulb thermometer for the temperature 

 of the air and the temperature of the dew-point, as found from the dry- and 



