406 



RECORD OF SCIENCE FOR 1887 AND 1888. 



Table V. — Total amount of heat received during the whole of March 21 or September 21, 

 at the equator, bij a square centimeter, exposed either horizontaUy or normally. 



1. Above the atmosphere and by a normal plate 



2. Above the atmosphere by a horizontal plate . 



3. At the earth's surface by a normal plate 



4. At the earth's surface by a horizontal plate . 



Calories. 



1. 2696 

 0. 8099 

 0.7159 

 0. 5441 



This last figure, 0.5441, is the unit of the following table : 



Tablk VI. — Solar heat received in twenty-four hours at various latitudes, in terms of the 

 amount received on March 21 at the equator, by a horizontal plate at the surface of the 

 earth. 



(2) Evaporation. — The quautity of moisture evaporated throughout 

 the whole globe must be equivalent to the total precipitation of rain, 

 isuow, etc., otherwise there would be a steady increase or diminution 

 iustead of the present condition of approximate equilibrium ; but the 

 local variations and irregularities in the distribution of this moisture 

 are very great, and constitute a secondary cause of the periodical, diur- 

 nal, annual, and secular changes, variations in the weather, and espe- 

 cially of the non-periodical variations or the so-called storms, droughts, 

 etc. The periodical chauges in the evaporation are roughly indicated 

 by the figures in Table vii. (Omitted.) 



The Table vii, however, relates only to average periodical eflfects. In 

 order to compute the special cases of evaporation that are particularly 

 iuteresting in the study of the daily weather map recourse must be had 

 to the formula of Weilenmanu, or to its modifications by Stelling, and 

 more recently by Fitzgerald or to the observations by Eussell. 



It is very important to keep in mind the relative amounts of evapo. 

 ration going on in all portions of the country, and it is recommended 

 to enter upon various portions of the weather map, on the scale of 10 

 or 100, some number expressing in a general way the probable relative 

 activity during the coming twenty-four hours. In the compilation of 

 such a set of numbers Tables vii, viii, ix, x, xii (omitted) are furnished 

 as helps to a rapid approximation. 



(3) Absorption; (4) Convection; (5) Radiation; (6) Conduction. — The 

 quality and amount of heat absorbed by the earth and afterward given 



