110 



of 147, which reduces the arc within which the resultant is to be 

 sought to 31; and this is the closest result that has yet come out 

 from absolute observation. This arc is within the limits of each of 

 the larger arcs that come out from the previous observations, and it 

 extends from 46 to 77 E. of the magnetic north. 

 , The currents in all the cases cited were not confined to the limiting 

 lines, but were constantly found in one or more of the intermediate 

 lines, and always in a direction consistent with the view taken. In 

 the last case, where the arc is reduced to 31, and in most of the 

 observations tabulated, the current in the limiting lines was so strong 

 that the author felt himself fully justified in concluding that if he 

 had lines of telegraph beyond these limiting lines, he should have 

 found currents : he has assumed 10 as not likely to be beyond the 

 range ; and this reduces the arc to 11; and knowing from expe- 

 rience in which limiting line the current is apt to be more active, he 

 has divided the arc of 1 1 into the proportion of 7 to 4 ; and has 

 set off a line, which may be taken to be a very close approximation 

 to the direction in which the currents move. It falls 63 E. of 

 magnetic N. ; and by deducting from this 21^, the value taken for 

 magnetic declination, the direction of the earth-currents, referred to 

 the astronomical meridian, is 41 j E. of N., or N.E. within 3|. 

 When the currents change in direction, it becomes S.W. within 3|. 

 The cases discussed go back as far as 1857 ; and there appears 

 to have been the same general direction during that period. A N.W. 

 and S.E. direction for the resultant is not known. 



The author discusses, as well as he can from the few data before 

 him, a few observations made in France and Switzerland. They are 

 meagre in detail, but confirm the impression, which would naturally 

 arise, that some such general direction will be found there. He also 

 refers back to Mr. Barlow's paper, in which an arc of 47 was ob- 

 tained, and within which the N.E. bearing was situated, being 30 

 from one limit of the arc and 1 7 from the other ; showing that 

 from the year 1848 to the present time no great change in azimuth 

 has taken place. 



A few remarks follow in explanation of certain specialities and 

 anomalies in the behaviour of some of the lines in respect to their 

 azimuths, and on the relative conductive power of the various geolo- 

 gical strata concerned. And the author thinks it very probable that 

 many of the currents, observed some thirty years ago in the metal- 



