Biography
of John Dalton
 John Dalton, detail of an engraving by W. Worhington,
after a portrait by William Allen, 1814 |
Dalton, John (b. Sept. 6, 1766, Eaglesfield, Cumberland.
Eng.- d. July 27, 1844, Manchester), British chemist and physicist who developed
the atomic theory of matter and hence is known as one of the fathers of modern
physical science.
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 layman and candidates for the ministry, the doors 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 1788, he began
observations about aurora phenomena - luminous, sometimes colored 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."
Color
Blindness
color blindness, inability
to distinguish one or more of the three colors red, green, and blue. (Ability
to see color exists in only a few vertebrates, including, among others, man
and the other primates, fish, amphibians, some reptiles, and some birds; and
in bees and butterflies.) In the retina, the light-sensitive layer of tissue
that lines the back and sides of the eyeball, there are, in human beings,
three types of cones, the visual cells that function in the perception of
color. One type absorbs light best in wavelengths of blue-violet and another
in the wavelengths of green. The third type is most sensitive to wavelengths
of yellow but is also sensitive to red.
Color-blind persons may be blind to one, two, or all of the colors red, green, and blue. (Blindness to red is called protanopia; to green, deuteranopia; and to blue, tritaopia.) Red-blind persons are ordinarily unable to distinguish between red and green, while blue-blind persons cannot distinguish between blue and yellow. Green-blind persons are unable to see the green part of the spectrum. Color blindness, which affects about 20 times as many males as females, is a sex-linked recessive characteristic. A woman must inherit the trait from both parents to be color-blind. A color-blind man and a woman of normal color vision have daughters who have normal color vision but are carriers of the trait that is, the daughters may have color-blind sons and daughters who are carriers. The sons of a color-blind man and a woman with normal vision themselves have normal vision and are unable to pass the color-blind trait on to offspring. The son of a normal man and a carrier woman may be color-blind, and the daughter of such a union may be a carrier. Thus, color blindness tends to skip generations. |
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, evaporation and 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 color 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 Colors" (1794),
in which he postulated that deficiency in color 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
color blindness.
An indefatigable investigator or 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 com-position 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. (A.B.Ga.)
BIBLIOGRAPHY. H.E. Roscoe, John
Dalton and the Rise of Modern Chemistry (1895), the most authoritative
biography, and with A. Harden. A New View of the Origin of Dalton's Atomic
Theory (1896), original material on Dalton's research: D.S.L. Cardwell
(ed.), John Dalton and the Progress of Science (1968); J.B. Conant and
L.K. Nash (eds.), Harvard Case Histories in Experimental Science, vol. 1
(1957), probably the most critical analysis of Dalton's work; Frank Greenaway. John
Dalton and the Atom (1966).
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