■50 WRITINGS OP JOSEPH HENRY. [1855- 



other causes. The progress of meteorology will call for an 

 increased number of observations of the proper character, 

 and for the repetition of the experiments with balloons, in 

 different parts of the earth. 



Celestial space, in which our sun and the earth and other 

 planets of our S3'stem are placed, is known; from different 

 considerations, to have a temperature of its own, which is 

 supposed to be the result of the inter-radiation of all the suns 

 and planets which exist in every part of the visible universe. 

 The temperature of this space is estimated to be about — 60°. 

 This fact being allowed, it will follow (since the heat at the 

 top of the air remains constant) that the rate of decrease of 

 temperature as we ascend will be diminished with the 

 decrease of temperature at the surface of the earth, and also 

 that the rate of decrease will follow a slightly diminishing 

 ratio. At all accessible elevations in the atmosphere how- 

 ever it may be considered as almost constant. In some 

 cases the rate of diminution is interfered with by abnormal 

 variations of temperature ; for example, as we ascend into the 

 region of the clouds, the latent heat evolved in the conden- 

 sation of the vapor produces a local heat in the atmosphere 

 beyond the natural temperature. In temperate latitudes it is 

 usual to allow 300 feet of elevation for the reduction of tem- 

 perature one degree of Fahrenheit's scale. This quantity 

 was deduced from thirty-eight observations collected by 

 Ramond. Boussingault found, from observation in the tropics, 

 the diminution at 335 feet. Col. Sykes, from mountain ob- 

 servations in India, the diminution at 332 feet. Saussure 

 ascertained the mean value in the Alps to be 271 feet. Gay 

 Lussac's celebrated voyage gave 335 feet. And the result 

 of several series of observations with the balloon by Mr. 

 Welch, under the direction of the British Association, omit- 

 ting the points unduly heated by the condensation of vapor, 

 was about 320 feet. In the construction of the isothermal 

 chart * we have adopted 333 feet, or three degrees to one 

 thousand feet, as the rate of diminution, and find in com- 

 paring the temperature of different places of varying heights 



*[See Map, at page 72.] 



