NO. 4 SOLAR RADIATION — ABBOT, FOWLE, AND ALDRICH 55 



method the observer, starting from sea level, measures the solar 

 radiation at highest sun under the most favorable circumstances, and 

 advances from one level to another, until he stands on the highest 

 practicable mountain peak. Thence he ascends in a balloon to the 

 highest level at which a man may live. Finally he commits his 

 instrument to a free balloon, and launches it to record automatically 

 the solar radiation as high as balloons may rise, and where the 

 atmospheric pressure is reduced to the twenty-fifth part of its sea 

 level value. All these observations have been made. They verify 

 the former conclusion ; for they indicate a value outside the atmos- 

 phere well within the previously ascertained limits of solar variation. 

 Our conclusion still is that the solar constant of radiation is 1.93 

 calories per sq. cm. per minute. 



