RECORD AND DISCUSSION OF TEMPERATURES. 



39 



The hours 7 A. M., 2 P. M., and 9 P. M., are those of the Mannheim Meteoro- 

 logical Society, adopted at the military posts of the United States and by the 

 Smithsonian Institution; the hours 3 and 9 A. M. and 3 and 9 P. M., are those 

 l^roposed by the Royal Society. Of the bi-hourly series, the observations at 10 

 A. M. and 10 P. M., will give a very close approximation; the sum of the squares 

 of the tabular monthly values is a maximum, and the temperature at these hours 

 does not change as rapidly as at other hours. Of the three-hour series, the hours 

 7, 2, and twice 9 are most convenient, but less accurate than the hours 6, 2, 10. 

 The hours 3 and 9 A. M. and P. M., have the least sum of the squares of the 

 monthly values; these hours are most suitable for cases having a sufficient number 

 of observers, or for fully oi'ganized expeditions. 



Solar Radiation. — After the return of light in the spring of 1854, a thermometer 

 was exposed to the direct action of the sun. On and after April 10th, the statical 

 measure by means of a black bulb thermometer was adopted. In connection with 

 these observations, the estimated amount of solar light was also noted. From a 



