The Campbell-Stokes recorder consists of a sphere of colorless or slightly yellow glass of a high degree of transparency. It is mounted in a frame in front of a concave surface set at focal distance from the glass sphere.[1] The central line of the recording chart must lie in the plane of the true meridian. The frame itself is adjustable to the sun’s altitude. The recording chart is graduated to hour intervals. The focal rays, shifting with the position of the sun, char a line along the chart. The charred line represents the duration of the sunshine. When the sunshine has occurred at short and irregular intervals the aggregate duaration may be found most quickly by placing the edge of a
Campbell-Stokes sunshine recorder.
sheet of paper along the record and marking thereon lengths equal to the lengths of the successive charrings. By sliding the paper along the trace, the lengths form a continuous line. Their aggregate then may be measured along the graduations of the paper.
- ↑ A sphere of the sort has some of the characteristics of a prism; it refracts the various components of a ray of light unequally—red rays the least, violet rays the most. The registering paper gives the best record, on the whole, when set at the focus of greatest light intensity. The best focal distance cannot always be determined by rule of thumb, however; it varies slightly with the locality, and therefore the optimum focal distance must be determined by the observer.
