430 



Mr. H. M. Tory on the 



It follows that the values of the difference-coefficients 

 obtained by reference to the AgF.P. are nearly the same, 

 and afford a convenient method of reduction at temperatures 

 near 1000° C. The S.B.P. difference-coefficients do not give 

 very good agreement at 1000° C. for impure wires. 



8. Method of Hey cock and Neville. — In the simple and 

 convenient method of reduction employed by Heycock and 

 Neville, the difference- coefficients for the various pyrometers 

 are calculated as usual from the S.B.P., but the reduction of 

 the observations from pt to t is effected by means of a single 

 difference-curve, drawn for the standard wire only, in terms 

 of pt as abscissa. The platinum temperature pt observed 

 with any pyrometer is reduced to the normal scale by taking 

 from the standard curve the difference t— pt corresponding 

 to the observed value oipt, and increasing it in the ratio d/d° 

 of the appropriate difference-coefficient d to the standard d°. 

 This method does not give absolute agreement with the 

 difference-formula (2) unless d=d°, but it often appears to 

 give more consistent results than (2) in the case of impure 

 wires at 1000° C, and it is simpler to apply, as it requires 

 only one difference-curve, which is drawn for the standard 

 wire. 



The following tables will show how close this agreement is 

 for three of the wires tested. The first column shows, for each 

 case, the temperatures for the standard wire corrected by the 

 difference-formula ; the second, headed Test, shows the corre- 

 sponding values for the impure wire, corrected by Heycock 

 and Neville's method. 



Table III. 

 Reduction by Heycock and Neville's Method. 



Standard. 



Test 

 No. (1). 



Standard. 



Test 

 No. (2). 



Standard. 



Test 

 No. (3). 



948-58 



94866 



9659 



968-9 



932-5 



932-9 



937 20 



938-16 



882-8 



884-9 



939 6 



939-8 



864-55 



864-55 



882-3 



884-5 



882-7 



882-6 



8o9-37 



839-10 



793-9 



795-4 



832-4 



832-1 



821-23 



821-24 



785-7 



787-1 



831-8 



831-6 



753-49 



753-51 



786-1 



787-3 



788-6 



788-6 



673-33 



673-22 



659-5 



660 



738-7 



738-5 



621-79 



621-72 



664-6 



664-8 



7290 



728-8 



61967 



619-61 



551-4 



551-3 



6759 



6756 



550S9 



550-32 



551-8 



5516 



623-2 



622-9 



54989 



549-81 



440-0 



443-7 



597-5 



597-3 



522-75 



522-88 







525-9 



525 6 



469-78 



419-86 



- 





• 



4799 

 434-0 



479-7 

 433 9 



