OF IRON, COPPER, AND GERMAN SILVER. 



547 



to take the curve in two or more sections, employing for each the proper 

 corresponding values of the constants. 



A conception of the relative value, for this purpose, of the two formula? may 

 be obtained from the two tables subjoined, showing the degree of approxima- 

 tion of the value of v, the temperature excess, as calculated by the formula, to 

 the value as given by the observational curve. The first, headed (F), is extracted 

 from Forbes' paper already quoted ; the second, headed (M), is the record of 

 one of my own experiments, along with the values of v calculated from formula 

 (B) ; while the third table, also headed (M), shows in how far the same experi- 

 mental results are approximated to by formula (A). These tables refer, of 

 course, to iron. 





I. 



;f>. 









v by formula 





x, in feet. 



v by experimental 

 curve. 



r = log A-- 



l+cx 



Difference. 





°C. 



°c. 











272-7 





025 



1905 



191-0 



+ 05 



05 



1347 



135-9 



+ 1-2 



075 



97-3 



98-23 



+ 093 



10 



720 



72-0 



00 



1-25 



53-6 







1-5 



408 



4021 



-0-59 



2-0 



24-2 



2358 



-067 



2:5 



148 



• > • 





30 



933 



908 



-025 



40 



40 



40 



00 



50 



1-8 



1-96 



+ 016 



60 



09 





. . ■ 



80 



0-28 



036 



008 



II. (M). 



x, in feet. 



v by experimental 

 curve. 



v by formula 



logv = log A + ex 



c + x 



Difference. 



00 



247-2 



2466 



-06 



0-25 



1721 



1738 



+ 1-7 



0-5 



125-25 



1255 



+ 0-25 



0-75 



923 



92-2 



-01 



1-25 



520 



520 



00 



1-75 



3035 



30-35 



00 



2-25 



182 



182 



00 



2-75 



1115 



111 



-005 



375 



43 



4-3 



00 



4-75 



1-85 



1-7 



-015 



5-75 



0-7 



07 



00 



