674 PROFESSOR THOMSON ON THE ELECTRO-DYNAMIC QUALITIES OF METALS. 
48. The gradual augmentation of the difference T^— Tg from its value at a time 
when the current had been flowing for eight minutes entering by the end next B, 
consequent upon reversing the current and letting it flow continuously entering by 
the end next A, is shown by the numbers at the foot of each table, as a mean result 
derived from a single experiment. The mean of the results of the three experiments 
is shown by the following numbers, and is exhibited by a curve in the Diagram (fig. 4) 
of § 57 below. 
Current entering by end next A. 
Time from instant 1 
of reversal in quarter- ^ 
minutes J 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
29 
30 
31 
32 
Mean Augmenta- ] 
MO 
MO 
00 
o 
iC 
CO 
to 
CO 
'CO 
MO 
CO 
!>• 
O 
00 
’rH 
CT) 
00 
CO 
CO 
00 
CO 
CO 
MO 
00 
CO 
0) 
CO 
CO 
oo 
MO 
C-O 
O Tfl 
MO 
o 
CO 
tioii of diiference > 
O 
o 
o 
»— 1 
CO 
lO 
CO 
CTi 
CO 
lO 
MO 
!>. 
00 
00 
oo 
o 
1— 1 
04 
CO CO 
CO 
Tfl 
T . T 
O 
o 
o 
o 
o 
o 
o 
o 
o 
O 
r-( 
r— i 
l-H 
04 
04 
04 04 
04 
04 
04 
04 
^ A J 
■ 
' 
• 
■ 
‘ 
* 
* 
■ 
* 
■ 
" 
• 
• 
' 
' 
’ 
49. That Vitreous Electricity carries heat with it in copper is indicated by each of 
the three experiments on the thirteen slip conductor adduced above, but by so narrow 
an effect ; amounting on an average to only 0°‘02 Cent., which corresponds to a 
reading of half that amount, or of a degree, being ^Q-th of a division on the 
scale of each thermometer; with such discrepancies among the results of the dif- 
ferent experiments (Oct. 28th, effect *039, Nov. 2nd, ’OHS, Nov. 26th, *01); and with 
so great fluctuations in the course of each experiment (see Tables I., II., III., § 56 
below) ; that I did not venture to draw from them so seemingly improbable a con- 
clusion, as that the convective effects in copper and in iron should be in contrary 
directions. The dynamic theory (§ 18) was fully satisfied by the demonstration 
which the experiments gave, that the convective effect is undoubtedly in iron a 
conveying of heat in the direction of the Resinous Electricity^ and that it is less in 
amount in copper, whether in the same direction as in iron or in the contrary direction. 
But it was still an object of great interest, (in fact an object of much greater interest 
than any verification of conclusions from the dynamic theory, which were in reality as 
certain before as after the experiments directly demonstrating them,) to ascertain the 
actual nature of the convective effect in copper, and I therefore endeavoured to make 
more decisive experiments for discovering it. 
50. The three experiments which had been made were quite sufficient to prove that 
the convective effect, whatever its true nature might be, was nearly insensible to my 
thermometers without either more powerful currents or a more sensitive conductor. 
To work with more powerful currents would have increased immensely the labour of 
carrying out the experiments, and would besides involve a large addition to the battery 
which had been used hitherto. I preferred therefore to make the conductor more 
sensitive, which I saw could be done by diminishing the body of metal in the tested 
parts, and so preventing the looked-for thermal effect from being so much conducted 
away from the localities of the thermometers as it had been. I accordingly had 
