7G 
MR. T. E. STANTON ON THE PASSAGE OF HEAT BETWEEN 
constant. To the upper end of this pipe a steel plate is attached, on the lower side 
of whicli the knife-edo’e of the extensometer bears, and which also carries the scale. 
The extensomete]’ consists of a Jong light lever working in a small bearing, at the 
top of the copper tul^e, the short end carrying a thin steel knife-edge, and the long- 
end extending to the scale. Jay means of which the extension of the copper pijae 
coidcl Jae measured. 
TJre extension was magnified by this means, so that a movement of 1 millim. of 
tlie pointer represented a change in the temperature of the pipe of 0'5°, with the 
result that the temperature of the pipe could Jae estimated to -njth of a degree. 
Before and after any experiment, the temperature corresponding to the given scale 
reading was determined Jay actual trial. All the pipes and the exposed parts of the 
apparatus were carefully lagged with cotton wool and sheet cork to prevent loss or 
reception of heat. 
Measurement of the Temperature of the Water. 
For this purpose carefully calibrated thermometers were used, of such a scale tJiat 
readings within i^^oth of a degree could Jae estimated. These were fixed in small 
brass chamJaers through which tlie water passed on entering and leaving the pipes, 
tlie cJiamJaers Jaeing carefully lagged and placed as near the pipe as possible. The 
chamiaers were fitted with smalJ stuffing boxes and screw glands to prevent leakage, 
and are shown in section in fig. 5. 
As the difference in pressure between the water entering the pipe and leaving it 
wns small, no correction was found necessary for the observed readings. 
In the experiments, at a pressure of about two atmospheres, it was found that the 
pressure had a small eflect on the thermometer readings, due to compression of the 
J^ulJ:), but this Avas not more than 0‘15° C. 
To measure the pressure, a “ Tee ” joint was connected to the top of the copper 
jtipe, as shown in fig. 4. This “tee” carried the extensometer lever in the centre, 
one binncJi being connected to the water supply, and the other branch being con¬ 
nected to a mercury pressure gauge in the form of a U-tube. 
To regulate the pressure to any desired amount, brass cocks were attached to the 
waste pipes leading from the pipe and jacket, Avhich could be adjusted to produce the 
in'essure. 
The joint between the coijper tube and the jacket pipe at the upper end was made 
Jjy an india-rubJ^er AvasJier and screwed cap, so as to allow free expansion of the pipe. 
At the loAver ends, tvhere the pipe Avas fixed to the standard, tlie jacket pipe and 
inner pipe Avere soldered together. 
Method of Making an Experiment. 
In the first place, the inside of the pipe Avas cleaned by a small brush, tJien the 
val\ns Avere set so tliat the recpiired amount of Avater AAms passing tlirougli the pipe 
