648 FREDERICK GUTHRIE ON THE THERMAL RESISTANCE OF LIQUIDS. 
worthiness of the instrument, for it shows the absence of convection from whatever 
cause. 
V. Measurement of the Velocity of Heat-penetration , t. 
§ 43. The question as to the rate at which heat passes through liquids immediately 
involves another, namely : — Does the effect of a greater heat-difference travel faster than 
that of a less heat-difference 1 This interesting question may be easily and satisfactorily 
answered by L means of the diathermometer. The conditions of an experiment were 
(with water) : — 
T: 
:21°-39 
: 3 millims. 
AT. 
30-83 
25-83 
20-83 
15-83 
10-83 
5-83 
(i) 
s 
7 
8 
8 
9 
10 
12 
( 2 ) 
S 
7 
7 
8 
9 
10 
10 
(3) 
s 
7 
8 
8 
9 
10 
11 
(4) 
s 
6 
8 
8 
11 
(5.) 
S 
7 
7 
8 
Mean. 
t. 
s 
6-8 
7- 6 
8 - 0 
9-0 
10-0 
11-0 
It appears distinctly from this Table that when the temperature-difference is greater 
a more rapid passage of the heat is effected, at all events when the same initial tempe- 
rature T is taken. There still remains, however, a possibility that the effect may be 
due as much to the difference of the quality of the heat at the higher limit as to the 
extent of the range. Perhaps there may be no simpler exact means of clearing up this 
point than the performance of similar experiments, at times when the atmospheric 
temperature has greatly altered. We shall return to this point in considering the 
quantity of heat which traverses the liquid disk. 
§ 41. When the temperature-difference is small the commencement of the effect is 
not well marked ; hence the tendency of the observer is to overestimate the time ; this 
error is diminished by using a very narrow tube for Q. 
§ 45. Sperm-oil and glycerine were examined under the following conditions : — 
T =26-5 
Sperm-oil . 
Glycerine 
AT =10-0 
§ = 3 millims. 
s 
17 
11 
'i 
s 
16 
11 
Mean. 
t. 
s 
16-6 
11 
We shall find subsequently that the resistances of the three liquids, water, glycerine. 
