Mr. J. J. Waterston, in 1857, made at Bombay some experiments on the
photographic power of the sun’s direct light, to obtain data in an
inquiry as to the possibility of measuring the diameter of the sun to
a very minute fraction of a second, by combining photography with the
principle of the electric telegraph; the first to measure the element
space, the latter the element time. The result is that about 1/20000th
of a second is sufficient exposure to the direct light of the sun to
obtain a distinct mark on a sensitive collodion plate, when developed
by the usual processes; and the duration of the sun’s full action on
any one point is about 1/9000th of a second.
M. Schatt, a young painter of Berlin, after 1500 experiments, succeeded
in establishing a scale of all the shades of black which the action of
the sun produces on photographic paper; so that by comparing the shade
obtained at any given moment on a certain paper with that indicated on
the scale, the exact force of the sun’s light may be determined.