124 Earth Currents and Electric Traction. [April 14, 



WEEKLY EVENING MEETING, 



Friday, April 14, 1899. 



Sir William Crookes, F.R.S., Vice-President, in the Chair. 



Professor A. W. Eucker, M.A. D.Sc. Sec.R.S. M.B.L 



Earth Currents and Electric Traction. 



Discussing the cause of the earth's magnetism, the lecturer said it 

 might be due to the existence of electric currents at a considerable 

 distance below the surface or to the presence of magnetised material 

 within the earth. He described the magnetarium constructed by 

 Mr. Henry Wilde in accordance with the latter hypothesis and the 

 means by which he was able to reproduce on a suitably arranged 

 geographical globe the magnetic condition of the earth as observed 

 in nature. He came to the conclusion, after an examination of the 

 difficulties involved, that the hypothesis must be admitted to be at 

 least one that was not physically impossible. Turning next to the 

 artificial surface currents such as resulted from electric railways, he 

 pointed out how dangerous they were to magnetic observatories. 

 This danger was first experienced in America, where rough methods 

 of construction had produced great disturbances, the observatories at 

 Washington and Toronto having been ruined from this cause. 

 Doubtless construction both in England and America had greatly 

 improved, but that did not end the matter, for it was not certain that 

 the most careful construction could entirely prevent the evil. The 

 engineers concerned in the various industrial enterprises had received 

 those connected with the observations very kindly and had agreed to 

 practice certain precautions, such as not putting currents to earth 

 and providing for insulated return wires. Still the next year or two 

 must be an anxious time, since if these measures proved inefficient, 

 the observatories would have to be moved, and a break be caused in 

 the observations of which it was very important to preserve the con- 

 tinuity. In conclusion he discussed the possibility of the existence 

 of currents between earth and air. 



