362 MR BALFOUR STEWART ON EARTH-CURRENTS DURING MAGNETIC CALMS, 



TABLE III. — Observations during Greater and more Abrupt Disturbances. 



Date. 



Time. 



Column 1. 



Column 2. 



Column 3. ' 



Dover — London, u. 

 London — Dover, d. 



Tonbridge — London, u. 

 London — Tonbridge, d. 



Dover— Tonbridge, u. 

 Tonbridge — Dover, d. 



1861. 





o 



o 



o 



Oct. 5 



7.44 A.M. 



35 d 



50 d 



45 d 



8 



3.12 P.M. 



48 u 



50 d 



55 u 



10 



3.14 ... 



30 u 



50 d 



50 u 



* 



10.0 ... 



55 d 



5 u 



10 d 



11 



6.25 A.M. 



55 u 



50 d 



55 u 





9.6 ... 



55 d 



35 u 



50 d 



24 



7.41 ... 



20 d 



20 u 



20 u 





7.54 ... 



15 u 



22 d 



35 u 





9.20 ... 



45 d 



25 u 



50 d 





9-37 ... 



55 d 



45 u 



55 d 



1 



10.25 ... 



30 d 



15 u 



43 d 





11.24 ... 







12 d 



8 u 





11.47 ... 



13 d 



25 u 



38 d 





12.29 P.M. 







15 d 









2.40 ... 



22 u 



65 u 



15 u 





2.44 ... 



55 u 



50 u 



50 u 







3.32 ... 



55 u 



13 d 



55 u 





4.23 ... 



7u 



35 u 









5.3 ... 



•3d 



32 u 



40 d 



..'. 25 



6.42 A.M. 



50 d 



20 u 



55 d 



... 28 



7.15 ... 







15 u 









12.13 P.M. 



20 d 



4 u 



27 d 





1.9 ... 



30 d 



14 u 



40 d 



Dec. 19 



8.18 ... 



... 



... 



55 d 



With the exception of the two cases noted, the declination and horizontal 

 force needles were in no instance very far from their normal positions. 



Let us now return to Table L, and endeavour by means of it to find the 

 normal values of the earth-currents for each of the three lines, corresponding to 

 the various hours of the day. And here it is necessary to remark that the 

 strength of the current is not strictly proportional to the angle of deflection noted 

 in the table, but rather to its tangent, which Mr Walker has kindly informed 

 me W'ill, in the case of his galvanometer, approximately represent the value of 

 the current. Taking therefore the tangents of the angles, and averaging the 

 results for each hour, we obtain the following tables, in which the sign + denotes 

 an up, and the sign - a down-current. 



* The declination needle was on this occasion considerably to the east of its normal position. 



