1904] Thermoelectric Power produced by Magnetisation. 431 



Curve (0) was obtained from a strip about 1*4 mm. wide and 

 0*75 mm. thick, which was cut from a rolled sheet purchased at a metal 

 warehouse. Curve (I) shows the retraction of a strip of the same 

 metal 9 mm. in width.* 



The fifth specimen was a wire taken from a piece of nickel gauze. 

 With this, too, the magnetised was found to be always thermoelectrically 

 positive to the unmagnetised metal. 



[A sixth specimen, consisting of a wire 3*5 mm. in diameter, has been 

 recently tested, with the same result. — May 23, 1904.] 



The form of curve (N) which rises to a maximum at about H = 150 

 suggested a possible source of error by which Thomson may have 

 been misled, and I therefore repeated his experiment. The arrange- 

 ment which is shown in fig. 8, is essentially the same as that employed 

 by Thomson. A piece of Griffin's impure wire was bent into the shape 

 of a horse-shoe, as shown, one of the limbs passing through the small 

 magnetising coil, PP; the ends of the horse-shoe were connected 

 by brass binding-screws to wires leading to the galvanometer T. Heat 

 was applied at or near Q by touching the wire with a hot copper rod, 

 and when the magnetising circuit was closed, the galvanometer T indi- 

 cated a thermo- current which usually had the same direction as in the 

 other experiments — from unmagnetised to magnetised through hot. It 



t(/ 



Fig. 8. 



was, however, found possible to adjust the strength of the field and 

 the position of Q so that a ther mo-current flowed in the opposite direc- 

 tion. This was the case, for example, when the field-strength was 400 

 and the distance of Q from the coil 8 cm. If a slight change were 

 made in the position of Q, the application of the same field again pro- 

 duced a current in the normal direction. This deceptive effect, which, 

 of course, really occurred between more strongly and less strongly 

 magnetised portions of the metal, could not be obtained with the pure 

 nickel wire, nor with the wire taken from the gauze, which were the 

 only other specimens tested. With an iron wire, however, it was quite 

 easily produced. 



Curve (m), fig. 7, shows in ten-millionths of length the mechanical 

 compression due to magnetisation ; in comparison with that for iron, 

 * Loe, cit., p. 214, fig. 4. 



2 H 2 



