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William de Wiveleslie Abney was an English scientist who made significant contributions to several fields of science including photography and vision science. He was a pioneering photographer with an interest in chemistry and was able to use these skills to advance knowledge in other fields that interested him, including astronomy. He married twice. In 1864, he married Agnes Matilda Smith with whom he had a son and two daughters. She died in 1888, and two years later, Abney married Mary Louisa Meade with whom he had another daughter. Abney died in December 1920 in Folkestone, England [1].
He was the son of a clergyman, Rev. Edward Henry Abney and his wife Katherine Strutt and was born in Derby (England). His father was interested in photography and was a friend of the pioneering English photographer William Henry Fox Talbot. William Abney and his brother Charles also got interested in photography and eventually became the founding members of the Derby Photographic Society in 1884. William attended Rossall School and the Royal Military Academy in Woolwich. He was commissioned in the Royal Engineers in 1861 and served in India through 1867. After his return to England, he was posted to the Royal Engineering School at Chatham, where he was promoted to Captain in 1873, and retired from service in 1881.
Abney was elected a Fellow of the Royal Society in 1876 and continued his career as an independent scientific investigator until his death. He was knighted in 1900 by Queen Victoria in England and served in several official capacities in science and education. These included assistant secretary to the Board of Education in 1899 and Director of the Science and Art Department in the UK in 1900.
46.1 Abney Effect
Arguably, Abney’s most significant contribution was in the field of photography. His introduction to photography at an early age gave him the impetus to examine, over the coming years, several related issues. His interest in photography was also encouraged during his service years at the Royal Engineers where he had the opportunity to offer a course in photography in Chatham. In 1871 and based on his lectures, he wrote a pioneering book, Instruction in Photography, which had its tenth edition published in 1900 [2]. In 1874, he traveled to Egypt to photograph the transit of Venus across the sun. He developed a dry gelatin photographic emulsion which he used in this expedition and which replaced “wet” emulsions. He also produced a book of photographs of historic temples at Thebes [3]. He wrote another book entitled A Treatise on Photography, which became a standard reference and also went into ten editions [4]. He discovered hydroquinone as a developing agent and silver bromide emulsions photographic printing on paper [5]. He is believed to have coined the term infrared. His knowledge of chemistry and his interest in astronomy resulted in developing an emulsion to capture the far-infrared solar spectrum in 1887 and the infrared spectra of organic molecules. Abney received the prestigious Rumford Medal from the Royal Society in 1882 “for his photographic researches and his discovery of the method of photographing the less refrangible part of the spectrum, especially the infrared region, also for his researches on the absorption of various compound bodies in this part of the spectrum” [6]. Abney’s contributions to photography also include modifications to the reciprocity law (based on the works of Robert Bunsen and Henry Roscoe in 1862) that govern the relationship between the intensity and duration of light required for the reaction in light-sensitive material [7]. Based on his observations Abney reported deviations from, and suggested improvements to, the law in 1893 [8].
- 1.
Visual and color science
Abney was a pioneer in researching sunlight in the atmosphere. He examined the visible spectrum and the transmission of light in different atmospheric media. He carried out a series of experiments on chromatic photometry in the 1880s. He also became interested in psychological aspects of color vision and the perception of spectral lights. These works resulted in publishing a book entitled Colour Vision, published in several editions through 1913 [9]. Among the topics examined by Abney were general issues associated with perception of color, e.g., disappearance of hue sensations with increasing eccentricity in the peripheral regions of the retina; color vision theories; role of color in visual science; and color perception under varied illumination conditions. Abney was a supporter of the trichromatic theory and did not believe in the opponent-color vision model. He also investigated several visual phenomena, which are still not completely understood. The most well-known of these observations is called Abney’s Law. This law describes that a compounded stimuli’s luminance is linearly and additively related to the luminance of its components. Abney proposed that the law is also applicable to brightness; however, it has been found that this is incorrect [10]. In addition, Abney described changes in visual appearance of light in the visual field because of exposure to sudden illumination, such as those in explosions [11]. Abney’s contributions also include the blur spot or “circle of confusion” in photography and microscopy and the invention of a camera for color photography.
- 2.
Abney effect
Abney discovered that perceived hue changes with increasing luminance of the stimuli. In other words, as the color becomes increasingly desaturated, it also changes in hue. The original article describing this phenomenon was published in Proceedings of the Royal Society of London, in 1909 [12]. The effect has since been known as the Abney effect. A simulation of this effect is depicted in Fig. 46.1. While desaturation of the color as a result of increased stimuli luminance can be relatively easily envisaged, a less intuitive effect is that of hue shift which as yet has not been satisfactorily explained. Abney decided to quantitatively examine these visual observations of color change. His investigation involved adding white light to mixtures of red, green, and blue primary as well as other lights. A single beam of light was split into two parallel beams projected onto a white screen. One beam was desaturated with a predetermined amount of white light (equivalent to half of the luminosity of the colored light) while the other was kept intact. He noted that the addition of white light caused the colored light to shift, from red to yellowish red, from orange to yellow–green, and from green to blue–green, etc. He concluded from his observations that the hue shift was mainly due to red and green components of the white light and that blue did not contribute much to the effect. Abney examined the percentage composition and luminosity found in the different spectral colors as well as the white light source that was added to the colored beams and experimentally matched the shifted colors based on calculated proportions [12].
Fig. 46.1A simulation of desaturation of colors by adding white light to illustrate the Abney effect