




304 Cc. G. KNOTT AND J. G. MACGREGOR ON THE 
(3.) Alloy containing 15 per cent. of Iridium. 
The deflections of the circuit containing this alloy being negative, it follows 
(from the arrangement of the circuits in these experiments) that the thermo- 
electric line of PtIr,, is above that of N on the diagram. From the observa- 
tions of the 3d column of Table VII. the following formula has been found :— 
§= —3'8992 + °314117¢+ 000283487’ . 
The 4th column of the same table contains the deflections calculated from this 
formula for various temperatures. They show the accuracy of the formula up 
to about 380° C. Hence 
= 31411 + 000566962. 
aay: 
If, therefore, t= Ors yo ell ; 
and if t=300° C., = ‘4842. 
The results of Table VIII. show that the relation between deflection and 
temperature of the M-N circuit is given by the formula 
6,=const. + °25577¢. 
Hence 
dp; 
a 25577 . 
All three circuits having exactly the same resistance, we have, therefore, 
dé : : nig : 
values of i for two temperatures which determine the position on the diagram 
1 
of the PtIr,; line. (See Plate X XI.) Its equation is found to be 
y= + '0443¢+ 67°86. 
(4.) Alloy containing 20 per cent. of Iridium. 
As in the last case, and for the same reasons, the thermo-electric line of 
PtIry on the diagram is above that of the N line. The observations recorded 
in the 5th column of Table VII. give the formula 
6 = —4:4606 + 3441474 (00012721? ; 
which is tested by the calculations contained in the 6th column, and found to 
be accurate up to nearly 380° C. Hence 
== ‘34414 + -00025442¢. 
ee 
If, therefore, t= 00 CO: yo Ostl4, 
and if t=300° C., © = 42047. 

