NIPHER— MAGNETIC DETERMINATIONS IN MISSOURI, 79. I43 



creasing or diminishing the magnetic intensity. The same expla- 

 nation he now apphes to rivers. 



My own explanation is as follows. Assuming the existence 

 of earth currents of electricity, the general direction of which is 

 from east to west, they distribute according to well-known laws, 

 flowing in greatest quantity through the lines of least resistance. 

 The magnetic needle tends to set at right angles to the current, 

 following the well-known law enunciated by Ampere. Where 

 the general direction of the moist river valley is at right angles 

 to the normal position of the magnetic needle, the position of the 

 latter is not changed, as the tendency of the needle is to set at 

 right angles to a current of electricity. In such a valley (as, 

 for instance, in the Missouri valley between Jefferson City and 

 the mouth of the river), the direction of the needle should be 

 normal, the direction in which the water flows being without 

 (appreciable) effect. 



Where the river runs at right angles to the earth currents, the 

 disturbing cause would be practically removed, as there would 

 be no deflected component of the earth current along the river 

 valley. 



The maximum effect is produced in the case of rivers making 

 an angle of 45 degs. with the general direction of the earth cur- 

 rents. Of course, this effect would be most marked where the 

 river and valley is very large, as in the case of the Mississippi 

 and Missouri, or where we have an immense drainage system 

 consisting of long rivers and creeks running parallel and in the 

 proper direction, as is the case on the eastern slope of Iowa. 



At present, the above explanation is suggested as a probable 

 one. During next summer it is the intention to make simulta- 

 neous determinations of the intensity of earth currents in the Mis- 

 souri valley and on the high prairie to the south. This will be 

 done by aid of private telegraph lines which will be built for the 

 purpose. It is the intention to put in a north and south, and an 

 east and west line at each station, making also simultaneous 

 declination determinations. By this means it is hoped that the 

 question may be solved. 



Whether the explanation above suggested be the true one or 

 not, the deffection of the 11" and 10° lines to the east in the west- 

 •ern part of Iowa, the abrupt bends between St. Joseph and Kan- 



