High speed and high resolution. Breakthrough ADC technology switches from 8 to 16 bits in the same oscilloscope.
The temperature (voltage) should be highest in the dark area beyond the red end of the spectrum or infrared (infra = Latin for below).
The heat drops off in the blue to violet part of the spectrum to the point where ultra violet you will not be able to distinguish it from the thermistor being in shadow.
My first graph done with PicoLog and plotted as a histogram was very similar to Herschel’s. When I automated the graph using PicoScope, the results were similar, but with a smoother tail on each side of the graph.
I ran the experiment from beyond the red to violet, so that my graph compared with Herschel's. It might be more exciting and surprising to run it the other way and watch the temperature go on rising when the thermistor is out of the visible spectrum.
An improvement to this experiment would be to use a motorized linear slide instead of the clock movement. The linear movement is better than the circular path of the clock, but is more difficult to achieve.