Principle
The temperature measurement shows that in the lower area of the glass the water temperature is practically constant (here 28 °C or 29 °C) only in a layer of 4 to 5 cm below the water surface does the temperature change by about 5 to 7. The colour distribution in the water also shows this temperature stratification. The experiment shows that water has only a low thermal conductivity, otherwise deeper heat layers would be warmed up more quickly. Energy transport always occurs in water through heat flow: heated water rises.