This animation illustrates the physical principle behind the operation of a calorimeter. On the right is an absorber with a thermometer to measure its temperature. On the left is a heat sink. The absorber and heat sink are joined by a thermal link.
The animation shows an X-ray hitting the absorber. As the X-ray enters the absorber, the mercury in the thermometer rises, indicating that a rise in temperature of the absorber. The heat from the absorber is transferred to the heat sink via the thermal link. As this happens the mercury in the thermometer decreases, indicating that the absorber is cooling.