John Dalton (1766 - 1844)
Dalton was the son of a Quaker weaver. When only 12 he took charge of a Quaker school in Cumberland and two years later taught with his brother at a school in Kendal, where he was to remain for 12 years. He then became a teacher of mathematics and natural philosophy at New College in Manchester, a college established by the Presbyterians to give a first-class education to both laymen and candidates for the ministry, the doors of the Universities of Cambridge and Oxford being open at that time only to members of the Church of England. He resigned this position in 1800 to become secretary of the Manchester Literary and Philosophical Society and served as a public and private teacher of mathematics and chemistry. In 1817 he became president of the Philosophical Society, an honorary office that he held until his death.
In the early days of his teaching, Dalton's way of life was influenced by a wealthy Quaker, a capable meteorologist and instrument maker, who interested him in the problems of mathematics and meteorology. His first scientific work, which he began in 1787 and continued until the end of his life, was to keep a diary--which was ultimately to contain 200,000 entries--of meteorological observations recording the changeable climate of the lake district in which he lived. In 1793 Dalton published Meteorological Observations and Essays. He then became interested in preparing collections of botanical and insect species. Stimulated by a spectacular aurora display in 1787, he began observations about aurora phenomena--luminous, sometimes coloured displays in the sky caused by electrical disturbances in the atmosphere. His writings on the aurora borealis reveal independent thinking unhampered by the conclusions of others. As Dalton himself notes, "Having been in my progress so often misled by taking for granted the results of others, I have determined to write as little as possible but what I can attest by my own experience." In his work on the aurora he concluded that some relationship must exist between the aurora beams and the Earth's magnetism: "Now, from the conclusions in the preceding sections, we are under the necessity of considering the beams of the aurora borealis of a ferruginous (iron-like) nature, because nothing else is known to be magnetic, and consequently, that there exists in the higher regions of the atmosphere an elastic fluid partaking of the properties of iron, or rather of magnetic steel, and that this fluid, doubtless from its magnetic property, assumes the form of cylindric beams."
Some of his studies in meteorology led him to conclusions about the origin of trade winds involving the Earth's rotation and variation in temperature--unaware, perhaps, that this theory had already been proposed in 1735 by George Hadley. These are only some of the subjects on which he wrote essays that he read before the Philosophical Society: others included such topics as the barometer, thermometer, hygrometer, rainfall, the formation of clouds, and evaporation and the distribution and character of atmospheric moisture, including the concept of the dew point. He was the first to confirm the theory that rain is caused not by any alteration in atmospheric pressure but by a diminution of temperature. In his studies with water he determined the point of the maximum density of water to be 42.5 °F (later shown to be 39.16 °F). Along with his other researches he also became interested in colour blindness, a condition that he and his brother shared. The results of this work were published in an essay, "Extraordinary Facts Relating to the Vision of Colours" (1794), in which he postulated that deficiency in colour perception was caused by discoloration of the liquid medium of the eyeball. Although Dalton's theory lost credence in his own lifetime, the meticulous, systematic nature of his research was so broadly recognized that Daltonism became a common term for colour blindness.
An indefatigable investigator and researcher, Dalton had an unusual talent for formulating a theory from a variety of data. The mental capacity of the man is illustrated by his major work that was to begin at the turn of the century--his work in chemistry. Although he taught chemistry for six years at New College, he had no experience in chemical research. He embarked on this study with the same intuitiveness, independence of mind, dedication, and genius for creative synthesis of a theory from the available facts that he had demonstrated in his other work. His early studies on gases led to development of the law of partial pressures (known as Dalton's law; q.v.), which states that the total pressure of a mixture of gases equals the sum of the pressures of the gases in the mixture, each gas acting independently. These experiments also resulted in his theory according to which gas expands as it rises in temperature (the so-called Charles's law, which should really be credited to Dalton). On the strength of the data gained in these studies he devised other experiments that proved the solubility of gases in water and the rate of diffusion of gases. His analysis of the atmosphere showed it to be constant in composition to 15,000 feet. He devised a system of chemical symbols and, having ascertained the relative weights of atoms (particles of matter), in 1803 arranged them into a table. In addition, he formulated the theory that a chemical combination of different elements occurs in simple numerical ratios by weight, which led to the development of the laws of definite and multiple proportions. Dalton discovered butylene and determined the composition of ether, finding its correct formula. Finally, he developed his masterpiece of synthesis--the atomic theory, the thesis that all elements are composed of tiny, indestructible particles called atoms that are all alike and have the same atomic weight.
Dalton's studies and writings, many included in his New System of Chemical Philosophy (part I, 1808; part II, 1810), cast light on the man. Dedicated to scientific research, independent in his approach, often diffident in seeking help in scientific papers that would aid him--or misguide him, as he often thought--he was a genius in synthesizing facts and ideas. Almost a recluse, with few friends, and unmarried, he was deeply dedicated to a search for the answer to scientific problems. His homemade equipment was crude, and his data were not usually exact, but they were good enough to give his alert and creative mind clues to the probable answer. Dalton remained a man of simple wants and uniform habits, keeping his dress and manners consistent with his Quaker faith.
Dalton's record keeping, although remarkable for quantity, often lacked exactness in dating, probably because he revised his manuscripts as secretary of the Philosophical Society between the time of the oral presentation and the publication. The exact date of some of his work, especially the atomic theory, is still in doubt because of this opportunity for revision. His documents were destroyed during the bombings of England in World War II. A fellow of the Royal Society, from whom he received the Gold Medal in 1826, and a corresponding member of the French Academy of Sciences, John Dalton was also cofounder of the British Association for the Advancement of Science. At his death more than 40,000 people came to Manchester to pay their final respects
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