I was reading a paper on the work of Count Rumford in developing the modern view of heat as a form of energy and not some kind of fluid. In that I encountered this experiment.
Say you had two cylinders B(say at temp. 100°C) and A(at 0°C). Now you place a thermoscope (which was at 50°C) in the middle.
The paper says that there was no change in the reading of the thermoscope as the heat gained from B was almost equal to heat lost to A.When they blackened the surface of B using a candle's flame they noticed that the reading of the thermoscope started to increase as the intensity of radiation from B got enhanced (I am not sure how ?).Now when they blackened both the cylinders they again saw no change in the temperature of the thermoscope which is unintuitive.
Rumford himself posed this question to the supporters of Caloric model of heat to explain the invariance in the temperature in the last scenario.
Now we have accepted heat as a form of energy. So how do we explain each of the above observations made by Rumford ?