East and West^ traversed hij an Electric Current. 32o 



of tlic wire, having in all cases observed vertical repulsion 

 duo to another cause than the earth's action — though he does 

 seem to have obtained an indication of the result he sought in 

 noticing that this repulsion was ^'not so much" when the 

 horizontal motion of the wire was towards the south as 

 when it moved northwards. Nevertheless, that a horizontal 

 wire should seem to become heavier when an electric current 

 is sent through it from east to west, and lighter when the 

 current is from west to east, follows so directly from our 

 whole theory of electro-magnetic relations, that years ago, 

 before I had read Faraday's papers above quoted, I had noted 

 down this point as one to be practically tested. I have lately 

 made the experiment, and with a result fully in accordance 

 with theory. 



A strip of light dry poplar (Liriodendron), 3 metres long, 

 25 millims. wide and 5 millims. thick , was placed horizontally 

 on edge, and served to support ten pieces of insulated (cotton- 

 covered) copper wire, 1 millim. in diameter, each piece a 

 little longer than the strip, these wires being carefully 

 stretched parallel to each other, five on each side the strip 

 toward the lower edge, and attached to the wood by little 

 cleats at the necessary intervals to prevent sagging. At each 

 end the wires were bent out horizontally so as to leave spaces 

 of about 20 millims. between them, and were then bent down- 

 wards at right angles and cut off so as to leave points like the 

 teeth of a rake about 40 millims. long ; these points were 

 amalgamated. This system of wires was supported in a hori- 

 zontal position from one arm of an excellent balance, slender 

 cords attached at several points along the strip being assem- 

 bled at a single ring, by which the whole was hooked on, and 

 counterpoised. 



The total weight was about 505 grms., the balance being- 

 capable of bearing a kilogramme in each pan, while turning 

 with a fraction of a milligramme. Two oblong blocks of hard 

 Avood were provided, each of which had sunk in the upper 

 surface a row of ten holes, 18 millims. in diameter and 30 

 millims. deep, at intervals of 20 millims. from centre to centre, . 

 to serve as so many independent mercury-cups in which the 

 ends of the long wires should dip ; a like number of small 

 holes bored obliquely, and communicating with the larger ones 

 at bottom, served to introduce the ends of the battery-wires. 

 These battery-wires were also insulated, ten in number, and 

 9 metres each in length, one of them being afterwards cut in 

 two in the middle. They were stretched parallel to each 

 other and near together on a light wooden frame forming 

 three sides of a horizontal square, of which the movable system 



