Young Physics
Georgina Garding
Young has been described as "The Last Man Who Knew Everything".[1] His work influenced that of William Herschel, Hermann von Helmholtz, James Clerk Maxwell, and Albert Einstein. Young is credited with establishing Christiaan Huygens' wave theory of light, in contrast to the corpuscular theory of Isaac Newton.[2] Young's work was subsequently supported by the work of Augustin-Jean Fresnel.[3]
Young belonged to a Quaker family of Milverton, Somerset, where he was born in 1773, the eldest of ten children.[4][5] By the age of fourteen, Young had learned Greek, Latin, French, Italian, Syriac, Samaritan Hebrew, Arabic, Biblical Aramaic, Persian, Turkish, and Ge'ez.[5][6]
Young began to study medicine in London at St Bartholomew's Hospital in 1792, moved to the University of Edinburgh Medical School in 1794, and a year later went to Gttingen, Lower Saxony, Germany, where he obtained the degree of doctor of medicine in 1796 from the University of Gttingen.[7] In 1797 he entered Emmanuel College, Cambridge.[8] In the same year he inherited the estate of his grand-uncle, Richard Brocklesby, which made him financially independent, and in 1799 he established himself as a physician at 48 Welbeck Street, London[5] (now recorded with a blue plaque). Young published many of his first academic articles anonymously to protect his reputation as a physician.[9]
In 1801, Young was appointed professor of natural philosophy (mainly physics) at the Royal Institution.[10] In two years, he delivered 91 lectures. In 1802, he was appointed foreign secretary of the Royal Society,[11] of which he had been elected a fellow in 1794.[12] He resigned his professorship in 1803, fearing that its duties would interfere with his medical practice. His lectures were published in 1807 in the Course of Lectures on Natural Philosophy and contain a number of anticipations of later theories.[5][13]
In 1811, Young became physician to St George's Hospital, and in 1814 he served on a committee appointed to consider the dangers involved in the general introduction of gas for lighting into London.[14] In 1816 he was secretary of a commission charged with ascertaining the precise length of the seconds pendulum (the length of a pendulum whose period is exactly 2 seconds), and in 1818 he became secretary to the Board of Longitude and superintendent of the HM Nautical Almanac Office.[5][15]
Young was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1822.[16] A few years before his death he became interested in life insurance,[17] and in 1827 he was chosen as one of the eight foreign associates of the French Academy of Sciences.[5] In the same year he became a first class corresponding member, living abroad, of the Royal Institute of the Netherlands.[18] In 1828, he was elected a foreign member of the Royal Swedish Academy of Sciences.[19]
Young died in his 56th year in London on 10 May 1829, having suffered recurrent attacks of "asthma". His autopsy revealed atherosclerosis of the aorta.[21] His body was buried in the graveyard of St. Giles Church at Farnborough, in the county of Kent. Westminster Abbey houses a white marble tablet in memory of Young,[22] bearing an epitaph by Hudson Gurney:[23][24]
Young was highly regarded by his friends and colleagues. He was said never to impose his knowledge, but if asked was able to answer even the most difficult scientific question with ease. Although very learned he had a reputation for sometimes having difficulty in communicating his knowledge. It was said by one of his contemporaries that, "His words were not those in familiar use, and the arrangement of his ideas seldom the same as those he conversed with. He was therefore worse calculated than any man I ever knew for the communication of knowledge."[25]
Though he sometimes dealt with religious topics of history in Egypt and wrote about the history of Christianity in Nubia, not much is known about Young's personal religious views.[26] On George Peacock's account, Young never spoke to him about morals, metaphysics or religion, though according to Young's wife, his attitudes showed that "his Quaker upbringing had strongly influenced his religious practices."[27] Authoritative sources have described Young in terms of a cultural Christian Quaker.[28][29]
Hudson Gurney informed that before his marriage, Young had to join the Church of England, and was baptized later.[30] Gurney stated that Young "retained a good deal of his old creed, and carried to his scriptural studies his habit of inquisition of languages and manners," rather than the habit of proselytism.[31] Yet, the day before his death, Young participated in religious sacraments; as reported in David Brewster's Edinburgh Journal of Science: "After some information concerning his affairs, and some instructions concerning the hierographical papers in his hands, he said that, perfectly aware of his situation, he had taken the sacraments of the church on the day preceding. His religious sentiments were by himself stated to be liberal, though orthodox. He had extensively studied the Scriptures, of which the precepts were deeply impressed upon his mind from his earliest years; and he evidenced the faith which he professed; in an unbending course of usefulness and rectitude."[32]
In Young's own judgment, of his many achievements the most important was to establish the wave theory of light set out by Christiaan Huygens in his Treatise on Light (1690).[33][34] To do so, he had to overcome the century-old view, expressed in the venerable Newton's Opticks, that light is a particle. Nevertheless, in the early 19th century Young put forth a number of theoretical reasons supporting the wave theory of light, and he developed two enduring demonstrations to support this viewpoint. With the ripple tank he demonstrated the idea of interference in the context of water waves. With Young's interference experiment, the predecessor of the double-slit experiment, he demonstrated interference in the context of light as a wave.
In his subsequent paper, titled Experiments and Calculations Relative to Physical Optics (1804), Young describes an experiment in which he placed a card measuring approximately 0.85 millimetres (0.033 in) in a beam of light from a single opening in a window and observed the fringes of colour in the shadow and to the sides of the card. He observed that placing another card in front or behind the narrow strip so as to prevent the light beam from striking one of its edges caused the fringes to disappear.[37] This supported the contention that light is composed of waves.[38]
Young performed and analysed a number of experiments, including interference of light from reflection off nearby pairs of micrometre grooves, from reflection off thin films of soap and oil, and from Newton's rings. He also performed two important diffraction experiments using fibres and long narrow strips. In his Course of Lectures on Natural Philosophy and the Mechanical Arts (1807) he gives Grimaldi credit for first observing the fringes in the shadow of an object placed in a beam of light. Within ten years, much of Young's work was reproduced and then extended by Augustin-Jean Fresnel.
The Young's modulus relates the stress (pressure) in a body to its associated strain (change in length as a ratio of the original length); that is, stress = E strain, for a uniaxially loaded specimen. Young's modulus is independent of the component under investigation; that is, it is an inherent material property (the term modulus refers to an inherent material property). Young's Modulus allowed, for the first time, prediction of the strain in a component subject to a known stress (and vice versa). Prior to Young's contribution, engineers were required to apply Hooke's F = kx relationship to identify the deformation (x) of a body subject to a known load (F), where the constant (k) is a function of both the geometry and material under consideration. Finding k required physical testing for any new component, as the F = kx relationship is a function of both geometry and material. Young's Modulus depends only on the material, not its geometry, thus allowing a revolution in engineering strategies.
Young's problems in sometimes not expressing himself clearly were shown by his own definition of the modulus: "The modulus of the elasticity of any substance is a column of the same substance, capable of producing a pressure on its base which is to the weight causing a certain degree of compression as the length of the substance is to the diminution of its length." When this explanation was put to the Lords of the Admiralty, their clerk wrote to Young saying "Though science is much respected by their Lordships and your paper is much esteemed, it is too learned ... in short it is not understood."[41]
In 1804, Young developed the theory of capillary phenomena on the principle of surface tension.[44] He also observed the constancy of the angle of contact of a liquid surface with a solid, and showed how from these two principles to deduce the phenomena of capillary action. In 1805, Pierre-Simon Laplace, the French philosopher, discovered the significance of meniscus radii with respect to capillary action.
In physiology Young made an important contribution to haemodynamics in the Croonian lecture for 1808 on the "Functions of the Heart and Arteries," where he derived a formula for the wave speed of the pulse[46] and his medical writings included An Introduction to Medical Literature, including a System of Practical Nosology (1813) and A Practical and Historical Treatise on Consumptive Diseases (1815).[5]
Young devised a rule of thumb for determining a child's drug dosage. Young's Rule states that the child dosage is equal to the adult dosage multiplied by the child's age in years, divided by the sum of 12 plus the child's age.
In an appendix to his 1796 Gttingen dissertation De corporis hvmani viribvs conservatricibvs there are four pages added proposing a universal phonetic alphabet (so as 'not to leave these pages blank'; lit.: "Ne vacuae starent hae paginae, libuit e praelectione ante disputationem habenda tabellam literarum vniuersalem raptim describere"). It includes 16 "pure" vowel symbols, nasal vowels, various consonants, and examples of these, drawn primarily from French and English.
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