TERRESTRIAL MAGNETISM. 215 



The farther calculation then gives : 



S = + 20° 28' log CO = 2-73907. 



i = + 66 43 

 ^fr = 1387"6, or, in the unity commonly employed, 

 yjr = 1-3876. 



29. 



The following table contains the comparison of our formulae, 

 with observations at 91 stations in all parts of the earth. As the 

 three maps from which we have taken the data for our calcu- 

 lation are intended to represent the phaenomena for the most 

 recent epoch, we have included in our comparison only very re- 

 cent observations, and we have taken, by preference, observations 

 at those stations where aU the three magnetic elements were ob- 

 served. We are not at present in a condition to demand that 

 the observations should be strictly cotemporaneous, unless we 

 would see our stock reduced to a very small number. 



