Friday, August 10, 2012

John Dalton: Atoms, Weather, and Vision

John Dalton
Since one of my undergraduate degrees was in chemistry, I cannot believe that to this point I have only written one post that warranted the tag of "chemists." So this post is an attempt to remedy this. In looking at the lists of names that I have as potential subjects for blog posts, the first that jumped out at me were Henderson and Hasselbalch, famous for the equation for determining the pH of a buffer solution.  But I try to mix up the time periods that I write about, which either means that you, my readers, do not get bored or that you get horribly confused.  If it is the latter, I apologize.  I would have guessed that the Henderson-Hasselbalch equation was developed in the nineteenth century, but it ws actually in the 20th century, which eliminates them from consideration at the present time.  So instead, I have decided to write on John Dalton, of Dalton's Law of Partial Pressures, which you may (or may not) remember from high school chemistry. Dalton is also well known for his work in developing modern atomic theory.  Whether or not you know much about either of these topics, it is easy enough to find information on his contributions in these areas.  So I would like to focus in this post on two areas that receive less attention, his meteorological observations and studies on color blindness.

Dalton's System of Chemical Philosophy
Dalton's atomic and
molecular symbolism, from
A New System of Chemical Philosophy
Dalton’s interest in meteorology began while he was at school in Kendal, where he made the acquaintance of John Gough, who was nine years his senior.  It was he who first suggested that Dalton keep a meteorological journal.  Dalton made observations throughout his long life, including a measurement made the day before his death.  His first book of observations, Meteorological Observations and Essays, was published in 1793, with a second edition little changed from the first appearing in 1834.  While some of the book is simply his observations, he also included descriptions of many of the techniques used in making observations of the weather in use at the time.  He noted in the preface that “as the number of [barometers and thermometers] is increasing daily, many of them must fall into hands that are much unacquainted with their principles.”  In addition to writing about barometers, thermometers, hygrometers, thunderstorms, snows, winds, and the Aurorae Boreales, he also included essays regarding these phenomenon, particularly Aurora Borealis and its connection with magnetism.  It was his study of the atmosphere, a gas, that probably led to his interest in gases in general, which finally led him to his theories of atomic structure.  He also attempted to come up with the structures of many molecules, but was not always right since he didn’t know how much each atom actually weighed.  For instance, he thought that water was HO (one hydrogen atom and one oxygen atom) rather than H2O.

John Dalton also put much thought into color blindness, a condition that he suffered from. He gave a lecture at the Manchester Literary and Philosophical Society, of which he was a member, in 1794, describing the inconsistencies that he observed between how he saw color and how those around him saw colors.  He wrote to a friend that “the flowers of most of the Cranesbills appear to me in the day almost exactly sky blue, whilst others call them deep pink.” (The Worthies of Cumberland: John Dalton, p. 101) He also noted that his brother and he agreed on the colors of things, which to modern ears suggests that it was genetic color blindness.  Dalton suggested that the cause of the difference between  his vision and others was that the fluid in his eye was tinted blue.  As a true scientist, he suggested that his eyes should be dissected after his death to see if this was true.  It was not, but the eyes were preserved by the Manchester Literary and Philosophical Society and recently the DNA was examined, showing that Dalton lacked one of the three photopigments in the eye.  (If you wish to see the present state of his eyes and related images, I suggest you go to This theory of photopigments had been proposed by Thomas Young (1773-1829), one of Dalton’s contemporaries who established the wave theory of light, but even though Young’s view was more correct, color blindness has been historically called Daltonism. This just goes to show that you don’t have to be right to be remembered, you just have to be the first, or perhaps the clearest.

Selected Works by Dalton
References and further reading