INTERCHANGE OF HEAT VON BEZOLD 



38l 



In order to give the estimates here set forth their full value, it is 

 necessary to compare the consumption of heat in the processes 

 above enumerated with the quantity furnished by the sun within 

 the given time. 



Unfortunately here we find ourselves in a very difficult position, 

 since the solar constant or the number of gram-calories that one 

 square centimeter of surface at the outer limit of the atmosphere 

 receives in one minute when the rays of the sun fall perpendicu- 

 larly on it, has not yet been determined with certainty. 



The values that have been obtained for this constant, which I 

 will designate by 5 vary between the limits 1.763 and 4.O. 7 But 

 since the greater number lie between 2 and 3, therefore, in order to at 

 least have a definite proposition, I will here use the value 5 =» 2.5, 

 or if the equivalent constant be expressed in square meters and kilo- 

 grams and minutes as units, then 5 = 25 (kilogram-calories). 



Under this assumption the whole earth receives 25 iz r 2 units of 

 heat in one minute, where r expresses the radius of the globe includ- 

 ing its atmosphere. This quantity of heat is distributed over the 

 hemisphere illumined by the sun, that is to say, over a spherical sur- 

 face whose area is 2 7i r 2 and hence on the average the sun gives each 

 square meter of the hemisphere on which it shines 12.5 calories 

 per minute or 12.5 X 60 X 12 = 9000 calories per day since, ignor- 

 ing the eccentricity of the earth's orbit, the average length of the 

 day light is 12 hours for every point of the earth. 



This amount of heat would suffice to melt a layer of ice 11.84 

 cm. in thickness, or to evaporate a layer of water 15 mm. deep per 

 day; or 550 centimeters of water or 43 meters of ice per year. 



If by anticipation (see page 414) we add that the quantity of heat 

 entering and leaving the soil during one year can in an extreme case 

 evaporate a layer of 40 mm., and if in general we express all this 

 data for the whole earth uniformly by the depth of evaporated 

 water or melted ice we obtain the following table: 



CAN 



EVAPORATE 



WATER. 



CAN 



MELT ICE 



cm. 



The sunshine in one average day i . 5 



The sunshine in one whole year S5o.o 



The heat received and lost annually in the soil is less than ... 4.0 



The heat that warms the atmosphere by 1° 0.4 



The kinetic energy of the atmosphere is less than o. 08 



7 Chwolson: On the present state of actinometry, pp. 10 to 14. 



cm. 

 12. o 

 4325.o 

 31.6 



3-2 



0.6 



