Figure 6. Pyranometer, a sensor used to measure variations in solar radiation.
It is used with a recording device, the solarigraph. The principle of operation
of the pyranometer is that of the thermophile of the Dutch Willem Moll. This
principle was adapted by Dr. Ladislaw Gorczynski of the Meteorological Institute
of Varsovia in 1924. The instrument shown was probably made in the 1940's.