THERMO-ELECTRIC DIAGRAM FROM -200 C. TO 100° C. 



783 



the temperatures were very high, the parabola was slightly steeper on the hotter than 

 on the colder side," but he considers this as " within the limits of error." He bestowed 

 very great attention on iron, tracing its E.M.F. curve up to a white heat, but unfor- 

 tunately leaving the temperatures to be expressed by the E.M.F.s of two alloys called 

 N — M, taken at the same instants as those of Fe — N, the constitution of N being 

 15 per cent, iridium and 85 per cent, platinum, while that of M seems never to have 

 been determined. 



At this stage it seemed worth while to examine some of Tait's work, not merely by 

 " superposing" curves of experiment upon "a nest of parabolas with a common vertex 

 and axis," but by the methods I had already adopted. Here again one has to say 

 " unfortunately " Tait has hardly published a single set of observations, though all 

 coming from him must have been of the greatest value, and of these there must have 

 been a very great collection. However, by a careful search, I have discovered two sets 

 made by two of his student-assistants, Messrs J. Murray and J. C. Young, and recorded 

 in the Proc. of the Royal Society of Edinburgh, in Feb. 1871 : " Their first sets of 

 observations . . . were made with an iron-silver and an iron-platinum circuit working 

 opposite ways as a differential galvanometer. The resistances (including galvanometer 

 coils) were in this particular experiment 53*1 and 25 9 B.A. units respectively, so that 

 but very slight percentage changes could be produced in them by the elevation of 

 the junctions. ... To show the parabolas due to the separate circuits, and thus exhibit 

 the advantage of the method, I have requested the experimenters to break the circuits 

 alternatively after taking each reading of the complex arrangement, and take a rough 

 reading. The last four columns of the Table give the results ; but, as the temperatures 

 were probably slightly different from these in the first columns, no very direct com- 

 parison can be instituted. A glance at the 4th, 6th, and 8th columns, however, shows how 

 nearly a linear relation between temperature-difference of junctions and galvanometer 

 deflection has been arrived at in the composite arrangement, while the separate circuits 

 give marked parabolas." 



Murray and Young's Table. 





• 





Deflection 





Deflection 





Deflection 



Low Tem- 

 perature. 



High Tem- 

 perature. 



Pt-Fe, 



Ag-Fe. 



for Incre- 

 ment of 



Pt-Fe. 



for Incre- 

 ment of 



Ag-Fe. 



for Incre- 

 ment of 









10° C. 





10° C. 





10° C. 



12° 3 C. 



39-0 C. 



28-5 



10-67 



44- 



16-28 



17- 



632 





72- 



61-5 



1030 



96-0 



16-08 



36- 



6-03 





104- 



93-0 



10-14 



143-5 



15-55 



51-5 



5-61 





146-5 



136-5 



10-17 



202-5 



15-08 



68-0 



5-06 



12-6 



185- 



172-5 



10-0 



250-0 



14-50 



77-0 



4-46 





202-5 



190 5 



1003 



268-5 



14-13 



79-5 



4-18 



12-4 



229-5 



219-5 



10-11 



298-5 



13-74 



81-5 



374 





251-5 



239-0 



100 



318-0 



13-30 



81-0 



3-38 



12-5 



2630 



250-5 



10-0 



330-0 



13-16 



80-0 



3-19 



)! 



272-0 



260-0 



10-0 



337-0 



12-98 



80-0 



3-19 



