698 



EXPERIMENTS ON AMPERE'S LAWS. 



wise the lower portion of the hole may be filled up with sealing-wax, 

 the copper wire having been bent aside previously. A small groove 

 should be cut for the wire in the lower surface of the wood from 

 to e ; at e a hole is bored with the gimlet, through which the 

 wire passes upwards. The wire is placed in the groove, the end 

 drawn through the hole e /, pulled pretty tight, and the piece / g 

 finally bent as in the figure. At h, close to the side of the wider 

 hole a made by the centrebit, the end of a copper wire, l mm thick, 

 is stuck into the wood, bent at right angles at the edge of the hole 

 and fastened along the upper surface by twisting it round two wood 

 screws fixed in the wood. 



The various parts being thus prepared they are put together in 

 the following manner. The small glass tube c is filled with mercury 

 by means of a small pipette made of a piece of glass tubing drawn 



O 



II 



FIG. 352 C, D (an. proj., | real size). 



to a point ; the mercury should reach to within 2 or 3 mm from the 

 top. The small board with the tube is then placed upon the foot of 

 the frame, underneath the larger square suspended to the frame, and 

 moved until the aperture of the tube is exactly below the end of that 

 wire which projects from the middle of the side of the square. The 

 end of the wire should be quite close ,to the aperture of the 

 glass tube ; the height at which the square is kept suspended 

 must accordingly be adjusted by raising or lowering the thread 

 which holds it. When the proper position of the small board has 

 been found it is secured in its place by a few drops of sealing- 

 wax which are allowed to fall upon the sides of the board and also 

 upon the foot of the frame, as seen at s, s, fig. 352 A. Mercury is 

 then poured into the cavity a, and the square is lowered until both 

 ends of the wire dip into mercury, without however touching the 



