Thermo-electric Interpolation Formulce. 



471 



those of Barns- will be first employed. The measurements to 

 be used consist of very elaborate and painstaking direct com- 

 parisons of several 20 per cent, irido-platinum thermo-conples 

 with several porcelain bulb air-thermometers used under the 

 constant-pressure method. 



Quotations of, or rather interpolations in, his original data* 

 are given by Barusf later, as a basis from which to deduce 

 constants for his proposed equation 



«+«„=io P+QA +io I " +lJV -. 



Barus ? s numerical values for the constants are : 



e =45680 microvolts. 

 P =4-6515 „ 

 F = 2-849 



Q = 1-106. 10- 4 . 

 Q' = 3-01 .10- 3 . 



These constitute his " equation 3," for which e corresponds 

 to 20° C. The data and the deviations which I have computed 

 for it, viz. S = data — equation, are given in Table I. The 

 last column gives the deviations expressed in percentages, 



viz., 100=1, where E = e + <? + 1880. This value of E is 

 xLi 



adopted to make the percentages comparable with those in 



subsequent discussions. The number 1880 is 1730 + 150, 



which are the values of e and ?L 2 ° e of the next two pages. 



Table I. 

 Barns's American Journal of Science Data. 



t° 



e+e mv. 



e+e computed 



3 



ioo| 



Per cent. 



observed. 



from " Equ. 3." 



mv. 



c c. 















-150 









100 



+680 



653 



+27 



+111 



200 



1650 



1657 



-7 



-0-20 



300 



2760 



2788 



-28 



-0-60 



400 



3950 



3994 



-44 



-080 



600 



6560 



6551 



+9 



+0-11 



800 



9310 



9273 



+37 



+0-34 



1000 



12200 



12140 



+60 



+0-43 



* Barus, C, U.S. Geol. Surv. Bull. no. 54 (1889) ; Phil. Mag. xxxiv. 

 p. 1 (1892). 

 t Amer, Jour. Sci. xlviii. p. 332 (1894). See also xlvii. p. 366 (1894). 



