CONDITCTIYITIES OF lEON AND COPPER. 
575 
first calculated from the values of M, cWjdx, and S (cW/dt), and the diftusivity k, 
afterwards calculated by dividing by the proper values of (sd), the thermal capacity 
of unit volume of the material of the bar. 
To obtain the values of s and d the densities of the iron and copper were carefully 
determined in the usual way, and, as the iron was not pure its specific heat at different 
temperatures could not be obtained from previous results ; it was therefore determined 
by Bunsen’s calorimeter, as described below. For the specific heat of the copper 
the results given by Bede^ were adopted. 
It will be evident that if dOjdx and ddUlt are expressed in the same units, the 
absolute value of these units need not be known, hence, in what follows, temperatures 
are given in scale divisions (galvanometer deflections), and the absolute value of a 
scale division in degrees Centigrade has but little bearing on the results obtained. 
Iron. 
Table I. 1. —Table showing distribution of temperature along iron bar during steady 
state. 
Number of bole. 
Distance in centims. from fixed 
point at heated end. 
[,r.] 
Excess of temperature in 
scale divisions. 
[d.] 
1 
1-00 
539 
2 
3-00 
458 
.3 
.5-55 
375 
4 
8-55 
283 
5 
12-30 
221 
(1 
20-00 
130 
7 
27-65 
81 
8 
35-35 
50 
9 
45-60 
26 
10 
55-90 
14 
11 
66-20 
( 
12 
81-55 
4 
13 
96-95 
2 
(end of bar) 
103-20 
— 
Temperature of air. 83 scale divisions. 
Between 0° C. and 100° C., 1° C. =; 375 „ ,, 
„ 100° C. „ 200° C., 1° C. = 37 4 „ 
* ‘ Memoire.s couronnes cle I’Acad. de Bruxelles,’ vol. 27, p. 1. 
