304 
MEASUREMENT OF HIGH TEMPERATURES. 
[BULL 
.54. 
capillary bore for the small length 
d, where the two tubes are in con- 
tact, will only change the mean 
radius _R , and will be fully al- 
lowed for in measuring 
% 
in the 
manner indicated. (See p. 282.) 
Another way of making capil- 
lary tubes with large terminal 
ends is shown in the exaggerated 
diagrams Figs. 51 and 52. In 
Fig. 51 a smaller capillary tube 
g is inserted at c in the larger tube 
g a b. The latter is then drawn 
* down in the wire plate until c has 
J the requisite small diameter. 
I Again, a simple platinum wire c 
p may be inserted into the tube a b, 
I as Fig. 52 suggests. These forms 
& have the advantage as consisting 
c of uniform tubes without solder- 
% ing, so that the danger of leaks 
I where the terminals join the tube 
| is obviated. 
| Finally, the simplest and surest 
| method of decreasing the central 
ef capillary bore consists in rolling 
I down the central part in a wire- 
S rolling mill, the two rollers of 
| such a mill being appropriately 
g grooved. 
g Without passing judgmeut on 
14 any of these forms, it is clear 
that the simple capillary tube 
used in the above experiments 
can be made to subserve the pur- 
poses of thermal measurement 
in the way shown in Fig. 53. 
Here the ends c f c' of the plati- 
num capillary tube c' c c c' are 
surrounded by the larger tubes 
a b, and a current of cold water 
circulates with great rapidity 
from a into b across the septum. 
Knowing the temperature of the cold ends of the capillary (this being 
the temperature of the water in a and &), the correction meinber can be 
(958) 
