114 ME. C. V. WALEJSE ON MAGNETIC STOEMS AND EAETH-CTJEEENTS. 
I have made no reference in this communication to feeble currents, which are 
possibly at all times to be collected from the earth, and in which a periodicity has been 
traced, but have strictly confined myself to the larger disturbances, the concomitants of 
“ Magnetic Storms.” Nor have I made any attempt to trace the origin of these earth- 
currents, or to offer any theoretical views thereon. I find current-electricity in the 
eai’th in a very marked degree at certain times ; I simply take it as I find it, and 
endeavour to arrange the facts in some degree of order, so as to throw a little more 
light than we have heretofore possessed upon these interesting phenomena. I have 
touched very lightly upon terrestrial magnetism, and have given no suggestion as to 
the probable causes of disturbance, save in the one case that necessarily arises out of 
the present inquiry. Other infiuences than those exerted by electric currents upon 
magnets may or may not be in play ; but one thing is very certain, that at least a large 
portion of the motion presented by the magnetometers on storm-days is connected with 
the then prevalence of earth - currents ; and doubtless some portion of all the more 
regular and less violent disturbances may be more or less due to the same causes. At 
any rate, although we are considerably in the dark as to the forms of force in operation 
to make up the ivhole of the causes concerned in magnetic disturbance, we are yet quite 
certain that the current-form of force is at least in imrt concerned. But 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 Eoyal, side by 
side with those presented by the magnetometers. And doubtless should such combined 
results come at any future day under discussion, and the more so should they pass into 
the hands of General Sabine, he would devise a method of eliminating the values due 
to these known causes, that is, due to earth-currents absolutely collected, and would by 
so doing render the values thus corrected more manageable, and might get one step 
nearer towards penetrating into the more recondite causes of the earth’s magnetism and 
its variations. This will not be accomplished until Mr. Aiky’s suggestion is brought to 
bear, and the duties of a magnetic observatory shall be extended to the observation of 
earth-currents. I hope, ere long, that some attempts of this kind may be made. Preli- 
minary observations are necessary before endeavours are made to organize a system that 
shall admit of general application. An electrical survey of the mass of the earth pro- 
mises to be rich in results akin to those presented by the magnetic survey. They are 
e’vidently tmn phenomena. The magnetic survey requires three instruments and their 
adjuncts, and a considerable amount of delicate manipulation. An electrical suiTey 
would require, as far as one can yet see, a single instrument only, after the resultant 
line for the place had been determined, and no larger amount, if so large, of manipula- 
tive skill. 
