I2-06
Observe infrared radiation
The output from a commercial thermopile is connected to an audio oscillator (as in N1-05) such that the frequency of the oscillator is proportional to the temperature observed: the hotter the object the higher the pitch. Use various sources: ice, boiling water, liquid nitrogen, the floor, people, etc. This is only qualitative; the system is not calibrated.
N1, I2, PS1