109 



5-min. The observations, which embraced a period of 50 hours 42 

 minutes, show very nearly an equal duration of N. and S. currents, 

 the difference heing 21|- minutes in favour of the S. currents. The 

 mean duration of N. currents was 9'51 min. ; of S., 9*42 min. The 

 proportion of currents exceeding 45 in value to those below 45, 

 was as 1 to 6*49. The 15 to 20 currents are most in number; 

 then follow, in order, the 5 to 10; then the 10 to 15. The 

 mean value of the N. currents was 28'01 ; of the S., 26 0< 07. 



Mr. Walker then refers to the opinion of M. De la Rive, that the 

 S. currents are merely due to the secondary polarities acquired by 

 the earth-plates, and shows that it is not in accordance with the facts 

 here accumulated; for, from the results given, it would be hard 

 to say that either the N. or the S. currents exceed the other in 

 value ; and no one thing could here be said of the N. currents, 

 which might not, with equal truth and equal force, be said of the S. 

 currents. 



The remarks thus far have reference to a solitary telegraph group, 

 from which the general drift, but not the special direction of the 

 earth-currents, is gathered. The action produced might be equally 

 due to a current running in a direction many degrees to the right or 

 many degrees to the left of the direct line joining the two stations. 

 In illustration of this, a series of diagrams have been prepared, in the 

 first of which the lines of direction (referred to the magnetic meri- 

 dian) of all the telegraph groups are set off; in others, the lines 

 alone on which observations were made at a given time, are laid 

 down. In proportion as the two boundary lines in any case make 

 a greater angle with each other, the absolute direction of the current 

 is more nearly determined. Cases are given and discussed, and the 

 conclusions progressively arrived at, in order, as lines with a greater 

 angle occur, to give the dimensions and position of the arc of the ho- 

 rizon within which the resultant line of direction is situated. When 

 observations are obtained from only one line, the resultant is known 

 to be somewhere in one half of the horizon ; but the place is not 

 proximately defined. Frequent observations were made on a pair of 

 lines making an angle with each other of 74. This reduced the 

 limit within which the resultant was to be sought to 106. Other 

 observations were made on a pair of lines making an angle of 136, 

 which reduced the limit to 42. And finally, a table of observa- 

 tions is given, which were made upon a pair of lines making an angle 



