FREDERICK GTJTHRIE OK THE THERMAL RESISTANCE OF LIQUIDS. 645 
At greater distances, as we shall see, t may be as much as 20 s . This time-lapse 
cannot be due to the obstruction caused by the metal bases ; for, as hereafter shown, 
when nothing intervenes between them, that is, when they are in actual contact, the 
lapse of time between the influx of hot water into A and the depression in Q is im- 
measurably small. Even when (5=1 millim. the time-interval t is sensible. 
§ 35. These experiments alone might be considered sufficient to show that at these 
intervals, at all events, and with water the effect of radiation is practically nothing. 
The question, however, is so fundamentally important to the investigation that it was 
examined in another way. The experiment was made as before, with water between 
the plates, then a disk of Swedish filtering-paper exactly of the same size as the plati- 
num faces was introduced, and the experiment was repeated. In these experiments not 
only was the time-lapse required for the first effect noted, but the total depression in Q 
after 1, 2, and 3 seconds was observed. Let these depressions, measured in millimetres, 
be AH : , AH 2 , AH 3 respectively. We need not reduce these linear depressions to 
thermal units to recognize the smallness of the effect produced by the interposition of 
the paper. 
T=21 0, 22 
T 1 = 31°-22 
AT=10°-00 
t. 
§=3 millims. 
AH r 
ah 2 . 
ah 3 . 
s 
millims. 
millims. 
millims. 
Water without. 
) 10 
47-77 
77-21 
90-52 
paper disk. J 
1 10 
48-26 
79-62 
91-00 
Mean 
10 
48-01 
78-41 
90-76 
s 
millims. 
millims. 
millims. 
Water with ] 
L 10 
46-81 
77-21 
88-59 
paper disk. J 
' 10 
47-27 
75-76 
86-67 
Mean 
10 
47-04 
76-48 
87-63 
If we take into account the great thermal resistance of paper, and further, that the 
absolute bulk of the matter through which the heat has to pass is increased by the 
introduction of the paper, we are again led to the conclusion that the effect of radiation 
is negligible. 
§ 36. In a previous experiment with another set of cones having brass, faces, similar 
results were obtained. The distance between the cones was about 2T millims., but it 
was not exactly measured ; neither was the temperature of the air nor the time-lapse t. 
The depression is given up to the end of 10 minutes. 
T 1 =23 o, 06 
AT=14° circa. 
&=2T millims. circa. 
4 R 
MDCCCLXIX. 
