THERMAL CONDUCTIVITY OE WATER. 
539 
a layer of hot water on the top of a quantity of cold with the aid of a properly con¬ 
structed floater, and applying the finger outside at the place of separation, a space of 
separation of the hot from the colder water can, even in this rough way, be ascertained 
to be certainly not so thick as half a centimetre. 
Figs. 1 and 2 show also the arrangement of the thermometers employed. In each 
case four are used. Of these three have their bulbs horizontal. Each of these shows 
the temperature of the layer in which it is placed. The thermometers A and B in the 
Fig. 2, 
diagrams show the difference of temperature between the two sides of a stratum of 
the liquid a few centimetres (5 to 10 centims.) thick. The thermometer C is merely 
used to show that heat has been conducted down to the bottom of the portion of 
liquid under experiment, and is therefore being conducted out below. When the 
thermometer C begins to rise the experiment is at an end. 
The fourth thermometer, marked I in the diagrams, is called the integrating 
thermometer. It has a bulb 30 centims. long, which is placed vertically in the liquid. 
This thermometer is intended to show the whole quantity of heat that passes during 
MDCCCLXXXI. 4 A 
