204 
ME. H. L. CALLENDAR ON THE PRACTICAL 
Table XI.—Comparison of Platinum and Iron. 
Temperature Centigrade. 
Resistances reduced to 1 at 0° C. 
Differences between 
observed and calculated. 
By air 
thermometer. 
Formula (e). 
1 a log e 
By platinum 
wire. 
Formula (a). 
, It- Rn 
By iron wire. 
Formula ( a '). 
, R' - R' 
Simultaneous pairs 
observed. 
Iron 
calculated by 
Eqn. (e'). 
at log e 
Expressed in 
percentage 
of R'." 
Expressed in 
degrees of 
temperature 
Cent. 
Platiuum. 
Iron. 
Je R/-R o 10 °- 
t ~ log R r- 
P Ri —K 0 10 °* 
log R - 1 + pt 
O 
O 
7 
O 
0 
0 
0 
1 
1 
1 
0 
0 
35-57 
35-41 
32-8 
1-1225 
11732 
1-1724 
0-07 + 
0-14 + 
99-79 
99-79 
99-79 
1-3453 
1-5263 
1-5263 
0 
0 
173-3 
173-2 
190-3 
1-5990 
2-0036 
2-0057 
0T0- 
0-15- 
269-2 
266-5 
335-4 
1-9220 
2-7692 
2-7667 
0-09 + 
0-11 + 
364T 
355-0 
506-4 
2-2283 
3-6715 
3-6636 
0-21 + 
0-20 + 
470-9 
449-4 
726-0 
2-5548 
4-8396 
4-8342 
0-11 + 
0-09 + 
586-3 
544-5 
998-4 
2-8840 
6-2667 
6-2775 
0-18- 
0-14- 
640-9 
587-1 
1148-2 
3-0314 
7-0566 
7-0576 
o-oi- 
o-oi- 
It does not appear that any equally simple and convenient empirical formula could 
be found to represent the observations so closely. [For the explanation of the small 
deviations, see Appendix, p. 228.] 
Comparison of Platinum and Tin. 
Pure tin wire, diameter '025 centim. 
Coil wound on cylinder of asbestos in paraffin in a glass tube. 
Resistance of copper connexions '0150 B.A. 
Resistance in melting ice of platinum 7*8113, of tin 3*2425. 
In hypsometer steam at 100*34, platinum 10*520, tin 4*7268. 
Insulation resistance at 200° C., 170,000 B.A. 
Insulation resistance at 0° C., 300,000 B.A. 
Tin observed 
Tin calculated . 
Platinum 
Temperature 
Table of Results 
1*4599 1*4052 
1*4599 1*4057 
1*3474 1*3082 
100*34 89*1 
Means reduced. 
1*3086 1*2440 
1*3092 1*2438 
1*2376 1*1888 
68*7 54*6 
1*0711 2*168 
1*0714 2*000 
1*0576 1*710 
16*5 205*3 
The temperature coefficient of this platinum coil, taken from the observations in ice 
and steam, comes out *003462 : almost, within the limits of error, the same as for 
other specimens from the same reel. The chief difficulty encountered arose from the 
softness of the tin near its melting point. The last observation is rather uncertain, 
as the metal gave way before the temperature was sufficiently steady. The coil was 
