An actinograph is an instrument for measuring or estimating the amount of light available, in terms of its ability to expose

photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine ...

. That is, it measures the ''actinic'' or ''chemical'' intensity of light, as opposed to

radiometric Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which ...

or photometric amount of light. The earliest actinographs were 24-hour recording devices, using a rotating cylinder of photographic paper exposed through a wedged-shaped slit to record a graph of actinic light during the period of a day; hence the ''graph'' suffix in ''actinograph''. Such devices were developed and described by Robert Hunt, secretary of the

Royal Cornwall Polytechnic Society The Royal Cornwall Polytechnic Society (commonly known as The Poly) is an educational, cultural and scientific charity, as well as a local arts and cinema venue, based in Falmouth, Cornwall, England, United Kingdom. The Society exists to promot ...

in 1845, as an improvement on T. B. Jordan's 1839 ''Heliograph''. In 1888,

Ferdinand Hurter Ferdinand Hurter (15 March 1844 – 12 March 1898) was a Swiss industrial chemist who settled in England. He also carried out research into photography. Early life Ferdinand Hurter was born in Schaffhausen, Switzerland, the only son of Tobi ...

and

Vero Charles Driffield Vero Charles Driffield (7 May 1848 – 14 November 1915) was an English chemical engineer who also became involved in photographic research. Driffield was educated at Liverpool Collegiate and Sandbach Grammar School. He also attended a priv ...

patented a device for estimating the actinic power of sunlight and for computing exposure times and apertures for cameras, based on the plate speed, time of day, time of year, and latitude. These were

slide rule The slide rule is a mechanical analog computer which is used primarily for multiplication and division, and for functions such as exponents, roots, logarithms, and trigonometry. It is not typically designed for addition or subtraction, which ...

s, not measuring instruments, and did not produce a graph, but Hurter and Driffield adopted the same name for it. In 1911, Arthur William Clayden M.A. (Fellow of the Royal Meteorological Society and Principal of the Royal Albert Memorial University College of Exeter) developed a version of an actinograph for meteorologists, to observe and record the change of radiation.The actinograph: An instrument for observing and recording changes in radiation
(April 1911) Quarterly Journal of the Royal Meteorological Society 37 no. 158, pp, 163–168

References

Photography equipment {{photo-stub

See also

References