THE THERMO-ELECTRIC EFFECTS OF LONGITUDINAL STRESS IN IRON. 29 



allow the wire under test to pays. Passing through the hole, the wire 

 is bent at right angles and clamped by means of a screw against the 

 end- plate of the heating apparatus. At the middle of the apparatus 

 there is an outlet and an inlet for steam, which is led by glass tubes 

 from a large boiler and away to a water tank. Another piece of wire 

 (call it wire B) slightly shorter than A is placed alongside of, and 

 coupled with, the wire A by being tied together at one point with fine 

 annealed iron wire as firmly as possible. This forms the hot junction 

 and is put inside the axial hollow space. The other end of the piece 

 A is formed into a loop, to which is tied a rope for leaden weights 

 (each 1 kilo, in mass) hung on with the help of a small pulley. Near 

 the loop, the wire B is coupled in the saine way with a, third piece 

 of wire about 1 metre in length (call it wire C). The free end of the 

 wire A is again in the same way coupled with a fourth piece of wire 

 (call it wire Z>>), exactly similar to the wire C. The other extremities 

 of C and I) are joined to the leading copper wires, the junctions being 

 dipped in mercury contained in two small glass tubes, themselves 

 surrounded by mercury contained in a large test tube. To keep the 

 temperatures of the junctions as uniform as possible, they were still 

 further protected by a large mass of water, and finally put in a wooden 

 box, shut in on all sides except for two small entrance holes for the 



