The earliest heat flow sensor

In 1914, the first heat flow sensor used to directly measure heat flow in the field appeared. At that time, Professor henky of Germany wanted to measure the heat flow through the floor of the brewery. He covered the floor with 10cm thick cork, measured the temperature difference between the upper and lower sides of the cork and the thermal conductivity of the cork, so as to calculate the heat flow density

This is the birth of the earliest heat flow sensor