ON CERTAIN THEßMOELECTRIC EFFECTS OF STRESS IN IRON. 355 



change after the l(Higitudiiial tenswii lias been appHed and removed. 

 Tf e is tlie electromoth e force between tlie after-strained and unstrain- 

 ed wire, reckoned ]io^iti\'e wben the current flows from the after-strain- 

 ed to the unstrjiiiied through the lu^t junction, Ave ma\^ represent 

 the vahies in tlie l;ist cobuini of Table \\ . by tlio linear expression 



e ^ + 34 - 0.21 t 

 where t is tlie tem])er;itui-e in Centigrade degrees, and tlie unit is 1 

 microvoh. 'I'he de\iati()ii of tliis straight line from the curve drawn 

 tln-ough the points is well within the errors of ob.servation. It would 

 Ije unsafe to sttach any importance to the suggestion of t^vo vertices in 

 the tabulated numbers, indicating two neutral points, one al)ove and 

 one below 160° C. (6' = 0). 



Thomson, ( ohn, Ewing, and other investigators have worked 

 witli temperatures linver 1han the highest we used ; so that it is not 

 possible to make a thorough compai-ison between these earlier results 

 and ours. AVhere a satisfactory comparison can 1)e made there is 

 (■om])lete agreement. For example in Ewing's tirst set of experiinents, 

 tlie after-strained wire came out poî^itive to the unstrained wire with 

 \\\e. hot junction at 100°C. Our residt is c =- -|- 13. 



In his later series of experiments Pn^fessor Ewing was concerned 

 wliolly with the thermoeleotric lieluniour of iron wii-e under the com- 

 bined influence of stress and magnetization. He kept his hot junction 

 at a temperature of 160°(' ; and it will be noticed that the after-strained 

 wire comes out ^legalivc to tlie unstrained wire. Since however no 

 observation is recc^i-ded for an uinuagnetized wii'c, and since Professor 

 Jiving hiîiiself seems disposed to regard this negatiN-e character as due 

 to the magnetization, it is im])ossil)le to make a satisfictorv comparisoii. 

 The \alues of the eleetromotive forces given l)\- him are of the s:nne 

 oi-dei' of (juantity as that just given. 



Oui- experiments indicate a maximum current as occurring about 



