Chenustry and Physics. 235 
tricity. In such a valley (as, for instance, in the Missouri valle 
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. here 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 
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. 
hether the explanation above suggested be the true one or 
11° an 
g. 
vations made at Moncalieri (Piedmont) from 1871-78.—The con- 
clusions deduced by R. ) 
f the maynetic declination in Piedmont are as follows: he 
mean monthly variation of the declination attains a minimum in 
December. {it increases at first slowly, from December to Febru- 
since the article on pp. 200-205 was printed, he states that the 
values of M, the strength of the magnetic field, given in the 
ae should be multiplied by a constant factor which is nearly 
exact numerical results in regard to the new action as observ 
™m several different metals. 
