REPORT OP EXECUTIVE COMMITTEE. 71 



Thus, as the average result from the three epochs we have : 



Region. Quantity of electricity. 



60° N to 60° S / ^^^ areas of low pressure + 829 X 10* amperes. 



■ I For areas of high pressure — 638 X 10* amperes. 



(+ means upward electric currents ; — means downward electric currents.) 



The average effect of electric currents for the region 45° N. to 

 45° S. is on the east-west component of the earth's magnetic force, 

 o.ooi C. G. S. unit, or about one-fiftieth of the average value of this 

 component. The average effect on the horizontal intensity is about 

 one one-thousandth part — /. c. , on the order of the error of a field 

 determination. However, the average effect on the declination is 

 about 0.2°, about six times the error of a reduced field determina- 

 tion of the declination on land and about one to two times the error 

 of a determination at sea by the most approved methods. 



Another result of prime interest to the magnetist, geologist, and 

 geophysicist was deduced with the aid of the existing magnetic charts. 

 About 65 to 70 per cent of the total magnetization of the earth can be 

 referred to a uniform or homogeneous magnetization about a diameter 

 inclined 11.4° to the axis of rotation. Deducting this "primary" 

 portion, there is left a "secondary or residual field," representing 

 the want of uniformity in the distribution of the earth's magnetism. 

 This secondary field has been mapped out by the department for the 

 two epochs 1840-45 and 1880, the writer having mapped out, in 

 1896 and 1899, in a similar manner, this field for 1885. The same 

 general characteristics are exhibited for the three epochs. 



It is definitely shown that the residual permanent magnetic 

 field of the earth is not a heterogeneous one, such as it would 

 be if, for example, its formation were primarily to be referred 

 to the irregular distribution of magnetic materials in the earth's 

 crust. On the contrary, although the magnetic system is 

 somewhat complex, it is yet quite systematic in its structure, 

 consisting chiefly of two main magnetizations approximately 

 transverse to the axis of rotation. There is, therefore, a very 

 strong indication that this field is produced by some distinct 

 physical cause operating in the same general manner over the 

 entire earth. The hope is thus clearly held out that we may 

 still further resolve the residual field, starting with fundamental, 

 physical causes. The present belief is that the chief physical 

 cause of the residual field is to be referred to the distribution 

 of temperature within the stratum of the earth's crust here 

 concerned. 



For there is a very remarkable correspondence between the prin- 

 cipal features of the residual magnetic field and those exhibited on 



