264 



A. W. Davison 



Standardization of Galvanometer. S = 4000 o! ms. 



Average = .0000308 volts per mm. of scale of galvanometer. 



Construction of the thermo electric 'power diagram. As stated 

 above, a very convenient method of determining the resultant 

 electromotive force for any two metals at any temperatures con- 

 sists in plotting the thermo electric power lines of these metals, 

 with temperatures as abscissas, and "electromotive force in micro- 

 volts per one degree centigrade" as ordinates. After such a 

 diagram has been constructed, all that it is necessary to do in 

 order to find the electromotive force around a thermo-electric 

 circuit of any metals, M and M' , whose junctions are at t\ and 

 ti is to determine the area, with consideration of algebraic signs, 

 enclosed in the quadrilateral composed of the two thermo-electric 

 power lines of the metals, and lines drawn vertically at ti and ^. 

 This electromotive force is of course given in microvolts. 



For convenience and simplicity, the lines of all metals are 

 usually drawn upon one sheet, with the lead line, since lead does 

 not show the Thomson effect, as the base line. 



Now in drawing these lines, one has only to remember that 6 

 represents the ordinate at 0°, while 2c is the tangent of the angle 

 between the thermoelectric power line, and the horizontal. 



Thus in drawing the line for copper, "6" is equal to 1.2 micro- 

 volts, hence a point was located whose coordinates are (0, 1.2) 

 Since "c" = .01358 microvolts, a point was located at 300° whose 

 coordinates are (300, 9.26). The abscissa 9.26 was determined 

 as follows: ''c" was multiplied hy 2t {= 2 x 300) and this 

 result (8.06) was added to 1.2. Now by drawing a line connect- 

 ing these two points, the thermo-electric power line for copper 

 is complete. 



