Ill 



liferous veins in Cornwall, may have been veritable earth-currents, 

 and may have been coincident with magnetic storms. 



Having determined the proximate direction of earth-currents, Mr. 

 Walker referred to the magnetometers of an observatory merely as 

 magnets, in order to discover whether the magnetic disturbances at a 

 given time were in accordance with the known reaction of electric 

 currents and magnets. The Astronomer Royal, as well as General 

 Sabine, furnished him with the photograms from Greenwich and 

 Kew respectively, which he required for making the comparisons. 

 He has selected some cases of earth-currents, and has set them out 

 in curves, side by side with the Greenwich or Kew curves, and has 

 found a sufficient amount of coincidence to confirm the conclusion 

 that arises, and to encourage further inquiries. He has laid down 

 the position which the declinometer and the horizontal-force mag- 

 netometer would tend merely as magnets to assume under the in- 

 fluence of currents moving in the assigned direction, and has given 

 some extracts from the Greenwich observations in support of the 

 views he takes. 



The author has made no attempt to trace the origin of the currents 

 in question. He simply takes them as he finds them, and endeavours 

 to arrange them in some degree of order ; and he touches very lightly 

 upon terrestrial magnetism itself. He considers that, " although we 

 are considerably in the dark as to the forms of force in operation to 

 make up the whole of the causes concerned in magnetic disturbance, 

 we are yet quite certain that the current form of force is at least in 

 part concerned." And he adds, " We can collect this force and 

 measure it, and deal with it independently. We can receive the 

 results and record them photographically as foreshadowed by the 

 Astronomer Royal, side by side with those of the magnetometers. 

 And doubtless should such combined results come at any future day 

 under discussion and more so, should they pass into the hands of 

 General Sabine, a method would be devised of eliminating the value 

 due to these known causes, that is, due to earth-currents absolutely 

 collected, and thereby rendering the value thus corrected more 

 manageable ; and we might get one step nearer towards penetrating 

 into the more recondite causes of the earth's magnetism and its 

 variations." And this cannot be accomplished until Mr. Airy's 

 suggestion, of including the earth-currents in the observations of a 

 magnetic observatory, is realized. 



