424 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



In this table, I first use the ordinary method of presentation in 

 which one proceeds by equal differences of latitude in order to 

 simplify the comparison between the values computed by this 

 formula and those found by Spitaler and Batchelder. Later I 

 will give the similar table with the sine as the argument. 



From latitudes 20 to 50 , or 0.6 of the whole surface of the earth, 

 this table shows a surprising agreement between the computed 

 values and those deduced by Spitaler and Batchelder from obser- 

 vations and here united into general averages for the two hemi- 

 spheres or into holospheric averages. The error is nowhere more 

 than 0.2 C. within the given latitudes. 



It is only in the equatorial zone and in the higher latitudes that 

 the differences become larger and that too for explanable reasons, 

 so that thereby the empirical formula acquires higher interest. 



In the equatorial zone the computed temperatures are higher 

 than the observed. This is undoubtedly a consequence of the 

 larger cloudiness, since this depresses the temperatures in lower 

 latitudes, as also a consequence of the above mentioned influence 5 

 of the complex convection whereby heat is carried from this zone 

 into the two surrounding belts, so that the temperatures in the 

 equatorial zone proper must be lower, but those in the two neigh- 

 boring zones higher than would be suspected from the insolation 

 conditions. 



Since in higher latitudes the cloudiness hinders the terrestrial 

 radiation, therefore to this circumstance we must ascribe the fact 

 that the temperatures beyond 50 of latitude are higher than would 

 be expected from this formula. 



Moreover, the last column of table 111 containing the differences 

 between the values deduced from Spitaler and Batchelder for 

 similar latitudes shows that these differences are of about the same 

 size as the departures of the numbers computed by the formula 

 from those derived by these authors from observations, excepting 

 for the above-explained systematic differences in the equatorial 

 zone. 



Hence the formula reproduces the actual existing conditions with 

 surprising accuracy. 



The result of this study may therefore be expressed as follows: 



"A change of 5.2 thermal days in passing from one parallel of 

 latitude to another corresponds to a change of i°C. in the mean 

 temperature of the whole circle of latitude. " 



s See Mechanics of the Earth's Atmosphere, 189 1, p. 243, and this present 

 collection of translations, No. XIII. — C. A. 



