A Jordan sunshine recorder lets in sunlight through a small hole in a cylinder or a semicylinder onto
photosensitized paper set inside the cylinder on which traces are recorded. One common type has two hollow semicylinders arranged back to back with their flat surfaces facing east and west (Figure 7.2 (a)).
Each flat surface has a small hole in it. The Jordan sunshine recorder used by JMA is the same in principle,
but consists of a hollow cylinder with two holes as shown in Figure 7.2 (b). The instrument has its
cylinders inclined to the relevant latitude and their axes set in the meridional direction. Photosensitized
paper with a time scale printed on it is set in the cylinders in close contact with the inner surface. When
direct solar radiation enters through the hole, the paper records the movement of the sun as a line.
Sunshine duration is ascertained by measuring the length of time the paper was exposed to sunlight.