INTERCHANGE OF HEAT — VON BEZOLD 415 



The investigations carried out in the previous section of this 

 memoir have led to the following results: 



"The quantities of heat exchanged in [i. e., entering and leaving] 

 the solid earth are in general small as compared with those that are 

 required to evaporate the [local] precipitation. 



"In middle latitudes the knowledge of the earth temperatures 

 in spring and autumn, in connection with the knowledge of the 

 capacity for heat of the unit volume of the local soil, suffices for the 

 determination of the quantities of heat interchanged in the ground 

 in the course of the annual period." 



In these theorems, however, the following points must be con- 

 sidered : 



The earth temperature must be determined at least by decades, 

 still better by pentades during these seasons, if not for the whole 

 year : 



The observations should extend to at least 6 meters in depth 

 beginning at 5 centimeters befow the surface: 



The temperature should be determined for at least three points 

 within the upper meter arranged so that the successive distances 

 of the thermometers diminish with approach toward the surface. 



" Hourly observations of those thermometers on which the diurnal 

 period exerts an influence, at least during the hours after sunrise 

 and before sunset, are needed for the determination of the diurnal 

 exchange of heat." 



Continuous registrations for these strata are still more desirable, 

 but these will attain their full importance only when it at the 

 same time becomes possible even at large intervals of time to make 

 continuous determinations of the heat capacity of the unit volume 

 in these strata or at least to keep informed of their water content. 



In general all measurements of earth temperatures first acquire 

 their true value when the thermal capacity of the unit volume of 

 the local soil with its average moisture is directly determined. 



It is very desirable indeed that for all places for which we already 

 have observations of earth temperatures such determinations be 

 made as supplementary thereto. 19 



19 Relative to the exchange of heat in the ground compare also the follow- 

 ing memoirs by J. Schubert: Der jahrliche Gang der Luft und Boden-tem- 

 peratur im Freien und im Waldungen und der Warme-aust'ausch im Erd- 

 boden. Berlin, 1900. As also Der Warme-austausch im festen Erdboden, 

 im Gewassern und in der Atmosphare. Berlin 1906. [Note added 1906, 

 W. v. B.] 



