SYMHC Classics: John Dalton

Summary

Podcast Summary: Stuff You Missed in History Class – SYMHC Classics: John Dalton

Hosts: Holly Frey & Tracy V. Wilson
Original Air Date: January 20, 2021 (Classic episode rebroadcast on September 6, 2025)
Main Topic: The life and work of John Dalton, with a special focus on his pioneering study of color vision deficiency ("Daltonism")

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Episode Overview

This episode dives into the scientific legacy of John Dalton, known for his atomic theory and foundational work in chemistry and meteorology, but here primarily celebrated for his groundbreaking insights into color vision deficiency. Holly and Tracy use Dalton’s life to explore the evolution of scientific understanding about color perception, genetics of color vision anomalies, and Dalton’s exceptionally detailed, humorous, and intuitive self-experimentation.

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Key Discussion Points & Insights

The Universal Question of Color Perception

• Both hosts reminisce on childhood questions about whether others see colors the same way.
• Tracy shares a personal anecdote: “I asked the same question of my father...he did not see color the way the rest of grief did...” (04:23)
• This curiosity ties directly to Dalton’s own journey: Dalton did not initially realize he perceived colors differently until well into adulthood.

Scientific Terminology and Genetics of Color Vision Deficiency

• The hosts explain why the term "colorblindness" is falling out of favor, replaced with "color vision deficiency" for clarity (06:48).
• Tracy details prevalence based on a 2014 study, highlighting its X-chromosome linkage and higher frequency in boys, especially white boys (10:15).
• Genetics breakdown: Red-green CVD is X-linked (so more common in males), blue-yellow is autosomal dominant and not sex-linked (11:21).

Historical Context and Dalton’s Place in Science

• The phenomenon of color vision deficiency was noted before Dalton but never rigorously studied.
• Dalton’s 1794 paper, “Extraordinary Facts Relating to the Vision of Colors,” is recognized as the first systematic analysis. Tracy sets up context: “The first systematic analysis appears in 1793...and that brings us to John Dalton.” (13:11)

John Dalton’s Early Life and Career Trajectory

• Born September 5 or 6, 1766, to a Quaker family (13:11).
• Began teaching by age 12, eventually teaching at New College in Manchester, then becoming a private tutor to focus on scientific research (14:28).
• Initial scientific pursuits included meteorology; later, a key discovery in color vision arrived from botany studies (15:04).

Dalton's Pioneering Self-Study of Color Vision

The Discovery

• Trigger moment: Observing geraniums by candlelight; flowers perceived as blue in daylight turned red in candlelight, revealing the difference in his vision compared to others (22:12, 22:52).
• Dalton's brother shared these perceptions, leading to their investigations.

The Experiments

• Used a prism to separate light, asked participants how many colors they saw. Most saw six, Dalton only two or three (23:42).
  • Notable Quote (Dalton):

    "That part of the image which others call red appears to me little more than a shade or a defect of light." (24:33)

• Detailed, often amusing descriptions of his perceptions:
  • Crimson: “Crimson has a grave appearance, being the reverse of every showy and splendid color.” (25:06)
  • Blood: Appeared “bottle green” to him; couldn’t distinguish it from dirt stains.
• Explored responses from other people with similar vision, including the Harris family, concluding the trait was familial and more common in males (28:09-29:24).

Early Contributions to Genetics

• Appearances of CVD in male family members but not females led Dalton to suspect sex-based inheritance, foreshadowing later genetic discoveries (29:24-30:06).

Dalton's Theories about the Source of CVD

• Hypothesized a colored “humor” (fluid) in the eye filtered out certain color wavelengths, based on how things looked when seen through stained liquids (34:17).
• Tracy: “He came to this incorrect conclusion...that one of the humors of my eye must be a transparent but colored medium...” (34:17)
• Left instructions for his eyes to be dissected posthumously to test this theory (35:59).

Posthumous Science & Legacy

Dalton’s Death and Aftermath

• Dalton died July 27, 1844; public funeral drew 40,000 mourners (40:15).
• His eyes were dissected and preserved—no colored humor was found; tissues were perfectly clear (40:38).

Modern Analysis

• Centuries later, DNA analysis of Dalton’s eyes confirmed a diagnosis of deuteranopia (red-green color vision deficiency) (41:13).
• Dalton's preserved eyes remain on display at the Science and Industry Museum, Manchester (41:51).

Developments Beyond Dalton

• Thomas Young’s theory (1801): Three receptors for red, green, blue—essentially correct, but took decades more for the science to advance (36:35).
• 19th and 20th century advances: Identification of rods/cones, understanding of retina structure, and most recently, discovery of ganglion cells as a third photoreceptor type (42:02).

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Notable Quotes & Memorable Moments

• On Terminology:

  • Holly: “Colorblindness is a term that's falling out of favor because it's not really accurate. Colorblind suggests that somebody can't see color at all.” (06:48)

• Dalton, describing red:

  • “That part of the image which others call red appears to me little more than a shade or a defect of light.” (24:33)

• On observing differences in candlelight:

  • “This significant shift in their color due to lighting changes startled him and led him to make a quick study by asking a number of friends to look at these same flowers...” (22:12)

• On CVD inheritance:

  • “It is remarkable that I have not heard of one female subject to this peculiarity.” (29:24)

• On scientific speculation:

  • Tracy: “He came to this incorrect conclusion...that one of the humors of my eye must be a transparent but colored medium...” (34:17)

• Dalton’s legacy:

  • Tracy: “He is also sometimes called the father of chemistry.” (38:28)

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Important Timestamps

| Timestamp | Segment | |-----------|----------------------------------------------------------| | 02:40 | Episode theme intro: John Dalton and color vision | | 06:48 | Discussion on terminology: “colorblindness” vs. “CVD” | | 10:15 | 2014 study: Prevalence and genetics of CVD | | 13:11 | Dalton’s birth and early life | | 15:26 | Dalton’s early work in meteorology and science | | 22:12 | Dalton’s pivotal flower observation by candlelight | | 23:42 | Prism experiments—how Dalton perceived colors differently| | 24:33 | Dalton’s own descriptions (notable quote) | | 29:24 | Family studies and early insights into inheritance | | 34:17 | Dalton’s colored humor hypothesis and self-experiment | | 40:15 | Dalton’s death, posthumous dissection, and public honors| | 41:13 | DNA analysis confirming Dalton’s diagnosis | | 42:02 | Advances in vision science beyond Dalton |

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Final Thoughts

This episode balances Dalton’s chemistry legacy with his remarkable foray into self-observation, systematic study, and speculation about color vision. Holly and Tracy’s conversation combines scientific curiosity, personal anecdotes, and historical context, making Dalton’s story vivid, relatable, and informative for a contemporary audience.

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For listeners new to John Dalton, this episode offers not only a window into early color vision studies but also a model of how individual curiosity can lead to lasting scientific legacies.

Transcript

[Holly Fry]

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[Holly Fry]

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[Holly Fry]

John Dalton was born on September 5th or 6th, 1766 or 259 years ago today or possibly yesterday on the day this episode is coming out John Dalton was a physicist and a chemist, but he's also known for his discoveries related to color vision and color vision anomalies.

[Tracy V. Wilson]

Our episode on John Dalton is today's Saturday classic, and it originally came out on January 20th, 2021. Enjoy. Welcome to Stuff youf Missed in History Class, a production of iHeartRadio. Hello, and welcome to the podcast. I'm Holly Fry.

[Holly Fry]

And I'm Tracy V. Wilson.

[Tracy V. Wilson]

Tracy, I bet this happened to you. I know it happened to me. Like, you must have had those moments as a child where you thought you were being very insightful. I know I certainly did. Where I was like, how do I know that what I see is the same thing as other people see?

[Holly Fry]

I had this exact. Yes, yes. I also asked my mom one time. I was like, mom, how do we know that what I see as green is the same thing as what you see as green? And my mom, stay at home mom with two little children did not always have a lot of patience for weird questions. And she was like, it's the same. I'm not trying to drag my mom in any way.

[Tracy V. Wilson]

My mom was, like, very supportive of.

[Holly Fry]

Our creativity and attentive to our. But yeah, this was a case where I liked. I just asked her at a question she was not prepared for. Question time.

[Tracy V. Wilson]

Here is the thing. I asked the same question of my father, who I did not know, and I don't know that he knew at the time, did not see color the way the rest of grief did. So he was trying to describe things. And I just remember, I mean, I was probably like seven or eight already, kind of a smart aleck. And I was just like, okay, this is going nowhere. I'm out. So maybe just saying green is green was really a better route because that led to a lot of confusion in our lives for a moment until we finally put the pieces together.

[Holly Fry]

Right.

[Tracy V. Wilson]

And really what happened was that. And I don't mean to drag my father, but, like, he was career military, so he's now retired, but his clothes were, like, sort of prescribed for him. Sure. When he stopped being constantly on active duty and started picking out his own clothes, some things became readily apparent, which is that that does not go together. My dude. Yes. They look. They're practically the same color. Oh, we should address this.

[Holly Fry]

Right.

[Tracy V. Wilson]

We never knew for years when you're wearing, like, jeans and a plaid shirt in your off time and then a uniform, the rest of the time, it would never come up. No. We learned. But this curiosity about whether other people see the way that you see is really, what drives a lot of scientific discovery. And we are talking about somebody who was curious and did a lot of scientific discovery. But in the case of this subject, who was very well known and respected in his day, he just didn't think about how he or anyone else saw color until he kind of stumbled into it while studying plants and realizing that his vision might be different from other people. And that's John Dalton. And really, John Dalton is far more famous for his work in atomic theory and which builds the foundations of organic chemistry. But he also wrote one of the first really thorough descriptions of what he called anomalous vision, meaning that he realized he was not perceiving color in the same way as other people. And his descriptions are very entertaining. We're going to read some of them. So today we will talk a little bit about his life, but mostly about this sort of pocket in his scientific work where he made a brief foray into exploring the world of photoreceptors and color perception, Although he didn't use those words for it.

[Holly Fry]

Colorblindness is a term that's falling out of favor because it's not really accurate. Colorblind suggests that somebody can't see color at all. But most people who have historically been diagnosed with colorblindness can see colors. They just see them differently. So defective color vision or color vision deficiency are becoming more preferred terms. I feel like I see people describing themselves as colorblind still quite a lot. So this is something that's evolving.

[Tracy V. Wilson]

We're still kind of at the beginning of the scientific community shifting to these different terms just. And it's really about clarity more than anything else. Right. Like, no, you do see color. We'll talk about one exception, but just differently. So we need to make a clearer term for it that's not misleading. And color vision deficiency is the inability to distinguish specific colors. Red, green, and blue. And to be diagnosed as colorblind historically, or color vision deficient now, a person only needs to have an inability to distinguish one of these colors. But it is possible for someone who has color vision deficiency to be unable to distinguish all three.

[Holly Fry]

So in your retina, you have cells called rods which perceive light, and then three types of cells called cones. Cones are really the important factor here. They are the photoreceptive cells that enable us to perceive color. The human retina contains 6 million cones. Red sensing cones make up 60% of the total number of cone cells. Green sensing cones make up 30%. And blue sensing tones make up the remaining 10%.

[Tracy V. Wilson]

So if all of your cone Cells are functioning normally. You are said to have trichromacy, Meaning you can see three tri of these colors, and they combine to create standard vision. But it is also possible to have dichromacy with only two types of cone cells present or functioning, or even monochromacy where only one type of cone is functioning. Monochromacy is a little bit tricky because it can also be used to describe a scen where none of a person's cones are functioning. And a person who has monochromacy may have other vision issues as well. And monochromacy that we just talked about with no cone function is kind of the one variation in all of this, where the colorblind label would be actually pretty accurate because everything to them appears not in the rainbow of colors, but as a shade of gray.

[Holly Fry]

Most of the time. Dichromacy manifests itself in a way that a person can't see see a difference between red and green. And dichromacy of this nature is broken down into separate classifications based on which types of cones do and don't work in a person's retina. Protanopia describes a state of not being able to see red. And deuteranopia is a case where the red cones function but the green cones do not.

[Tracy V. Wilson]

Blue yellow color deficiency, which is a little rarer, is similarly broken down into classifications based on its specific nature in a given person. So someone with a lack of blue cones is said to have tritanopia. And if they have blue cones but reduce sensitivity to that color, it is actually described as tritanomaly.

[Holly Fry]

An all color vision deficiency can fall on a spectrum. Some people have a diminished ability to distinguish red from green, for example, but they're able to see difference within specific shades of these colors.

[Tracy V. Wilson]

Yeah, sometimes, you know, people can't hit the lighter tones or the darker tones get real muddy, but they can see different shades. It manifests in many different ways. And in the United states, an estimated 5 to 10% of the population have some form of color vision deficiency. Usually this gets tested for when people are kids, and more boys than girls have color vision deficiency, and the percentage shifts based on race. So there was a 2014 study that gets cited a lot. This was published in the journal Ophthalmology. And it had taken studies of the color vision of 4,000 California children ranging in age from 3 to 6. And in this study, it was found that among the girls, less than half a percent of them exhibited signs of color vision deficiency, regardless of race. But in boys, the numbers were different. Six percent of the white boys in the study were diagnosed with color vision deficiency. 3% of the Asian boys had some form of color vision deficiency. It was found in fewer than 3% of the Latino boys and less than 2% of black boys.

[Holly Fry]

Genetically, boys are more likely to have red green color vision deficiency because they only need to inherit it from their mother. It is a recessive characteristic that's associated with the X chromosome. So if a female inherits the trait from her mother but not her father, she'll generally have normal color vision. She only has that one X chromosome, but then she could pass the trait on to her own children. And this is different from blue, yellow color vision deficiency, which is a dominant characteristic. And so that only needs to be inherited from one parent, and it is not linked to a person's sex. We sh. I'm just gonna say these are related to sex and not to gender. That's a different thing.

[Tracy V. Wilson]

Yeah, we're going with kind of that 2014 study, Separation of Boys and Girls, which simplifies the whole discussion. And is. Is sex assigned at birth? Not necessarily. How if they did that, I would be fascinated if they did the same exact test today and how they would break it out, because things have shifted a bit. So if anybody knows of any studies similar to that going on today, I'm very curious. But here's the thing. You're probably wondering how we figured all of this out. And in the late 18th century, this idea of people perceiving color differently than most humans was certainly not unknown. King George iii, for example, reportedly discussed this with an English novelist, Fanny Burney, at court in 1785. And there were some theories about what caused color vision anomalies published in Germany in the late 1700s. But the first systematic analysis of color vision deficiency appears in 1793, at least the first that we know of. And that brings us to the person we mentioned at the top of the show. John Dalton.

[Holly Fry]

John Dalton was born in early September, 1766. His actual date of birth is either September 5th or September 6th. His parents, Joseph Dalton and Deborah Greenup Dalton, were Quakers. His father made a living as a weaver. The Daltons had three children who lived to adulthood, and John was the youngest of them.

[Tracy V. Wilson]

And as a child, John attended a Quaker school. And that school changed hands when John was 12. John Fletcher, the man who had been running it, gave it to John Dalton's older brother, Jonathan Dalton. And then Jonathan enlisted John's assistance in this new role. And this set John on a path as an educator, just kind of delights.

[Holly Fry]

Me that they had a John and a Jonathan.

[Tracy V. Wilson]

It makes me giggle as well.

[Holly Fry]

John and Jonathan expanded their new careers by taking over a school in Kendall, England when John was just 14. This was a larger operation than the Quaker Grammar school they had been running, and it included students who boarded as well as day students. This totaled about five dozen students in all. And John was sort of learning on the job. He was studying with scholars to learn math, Latin, Greek and science to stay ahead of his students and to be able to speak on the subjects of their curriculum.

[Tracy V. Wilson]

And keep in mind again, he's like 14, 15 at this point. So he is taking in a lot of information. And he stayed in that job for a dozen years. And then at the age of 27, John moved on to a new professional post as a mathematics teacher at New College. And this was in Manchester. And he found all this a little bit frustrating though, because his workload in that job prevented him from having time to pursue his own scientific study. So he switched gears and decided that he would become a private tutor so that he could manage his own time in a way that would enable him to carry on with his side work.

[Holly Fry]

At this point, his work outside of his daily teaching tasks was focused largely on meteorology. He had been publishing articles in the subject for several years, but he kept studying other sciences as well and all. And it was through these studies that he wound up writing a paper that expounded on the idea that not everyone saw colors in the same way.

[Tracy V. Wilson]

So this was not the first time the mention of non standard color vision appeared in print. As we said earlier, surely color vision deficiency has been in play almost as long as humans have existed. And even before Dalton, there had been some mentions of it, including a write up of a man named Thomas Harris that was published in Philosophical Transactions and that described Harris's inability to distinguish colors, which was published in 1777. We're going to come back to Harris and we'll talk first more about John Dalton. But before we do all of that, we're going to pause for a brief sponsor break.

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[Tracy V. Wilson]

John Dalton presented his paper with which was titled Extraordinary Facts Relating to the Vision of Colors with observations by Mr. John Dalton at Manchester's Literary and Philosophical Society on October 31, 1794. He had joined the Society upon moving to Manchester, and as scientific papers go, this one is kind of unique in that Dalton himself is really the subject of the paper, or at least his.

[Holly Fry]

Vision was that text opens with quote it has been observed that our ideas of colors, sounds, tastes, etc. Excited by the same object, maybe very different in themselves without our being aware of it. He goes on quote I was always of the opinion, though I might not often mention it, that several colors were injudiciously named. The term pink in reference to the flower of that name seemed proper enough, but when the term red was substituted for pink, I have thought it highly improper. It should have been blue in my apprehension, as pink and blue appear to me very nearly allied, whilst pink and red have scarcely any relation.

[Tracy V. Wilson]

He goes on in his introduction to mention how he had learned about light and optics in his scientific studies, but he hadn't really thought about applying any of that information to colors because that entire area, the idea of color, seemed kind of confused and odd to them. Like he really was like, why would people group these colors together? It doesn't make any sense, but I guess that's how we've always done. Was not until he turned his scientific work to botany that he really started thinking about why some color groupings just made no sense. And this study prompted him to ask other people questions about colors. He actually uses the example in this paper of asking a person whether a flower was blue or pink, but they always just thought he must be joking because the queries came off as so completely absurd to them. So he just thought everybody had this weird relationship with Col.

[Holly Fry]

Even though he thought colors made no sense, it didn't really occur to him to wonder if there was something unusual about the way he was perceiving colors. It was a moment in 1792, two years before he presented his paper, that really gave him this moment of pause. That moment happened when he was looking at a geranium by candlelight.

[Tracy V. Wilson]

So he had frequently seen these flowers. This particular variety he was looking at were in fact pink in daylight, and to him in daylight he perceived them as sky Blue, but by candlelight. He saw this flower as a vibrant red. And this significant shift in their color due to lighting changes startled him and led him to make a quick study by asking a number of friends to look at these same flowers in both daylight and candlelight. All of the people he initially asked about it saw them as pink in both lighting conditions, except for his brother, who perceived that same shift of them being sky blue in the day and red in candlelight.

[Holly Fry]

This experience caused him to start a more structured study of light and color, which he did with an assistant who had normal color vision. First, he used a prism to project sunlight into a dark room and then recorded the number of colors that various people saw in that band of light. Most of them saw six. Red, orange, yellow, green, blue, and purple. He does mention that purple is separated into indigo and violet. And Newton's writings on color. For the purposes of a person simply looking at a band of light, that distinction is really nominal. I think we talked about this in one of our episodes that touched on Newton previously. He put indigo and violet in there separately because he wanted there to be seven. So that's why people typically don't actually see them as two distinct shades in light from a prism.

[Tracy V. Wilson]

Yeah. Or you'll see what you think is maybe a slight difference, but it's hard to be sure. Yeah. So for. For Dalton, he just called that one thing. It's purple. When Dalton looked at the prismatic light, though, he could only make out two or sometimes three colors. So generally, he just saw yellow and blue. Or sometimes he would see yellow, blue, and a little bit of purple. And through his work, he identified that the band that he saw as yellow was where other people were seeing red, orange, yellow, and green. And he wrote, quote, that part of the image which others call red appears to me little more than a shade or a defect of light. After that, the orange, yellow, and green seem one color which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow.

[Holly Fry]

Dalton's perception of blue and purple aligned with what other people were seeing. And the contrast between the end of his band of yellow and the adjacent blue was really sharp.

[Tracy V. Wilson]

So next, he did the same collecting of perceptions from himself and others when looking at candlelight projected through a prism. And these results were mostly the same. The only exception that Dalton calls out is that, for him, the red edge of the image looks more vivid in candlelight than it did looking at sunlight under the same conditions of being put through a prism.

[Holly Fry]

Dalton's paper next breaks out studies of specific colors as he had always perceived them. He starts out by describing colors grouped with red as they appear in the daylight versus candlelight. His description of crimson is pretty charming. Quote. Crimson has a grave appearance, being the reverse of every showy and splendid color. A similarly quaint description is his description of pink. He breaks that down as 9 parts light blue and 1 part red. Quote or some other color which has no other effect than to make the light blue appear dull and faded a little. He also lists out all the flowers that to him look blue. To give the reader a sense of context when he says, he says pinks and reds as blue. Blood, he says, appears to him as the color most people call bottle green. And he mentions that if he saw a light colored stocking that was spattered with either fresh blood or dirt, he would not be able to tell the difference.

[Tracy V. Wilson]

Visually, I I love this entire paper so much. It's exactly like this the whole way through. His his turn of phrase is quite, quite charming and endearing. He goes on to describe the significant change that red undergoes for him when viewed in candlelight. He describes it as much more vivid and the blue no longer being present and instead replaced by yellow tones. While he found most reds and pinks quite drab by daylight, in candlelight they became really vivid and even exciting. Orange and yellow, he says, are not too different for him than anyone else.

[Holly Fry]

When he moves on to discussing green, he writes, quote, I take my standard idea from grass. This appears to me very little different from red. The face of a laurel leaf is a good match to a stick of sealing wax. Hence it will be immediately concluded that I see either red or green or both different from other people. The fact is, I believe that they both appear different to me from what they do to others.

[Tracy V. Wilson]

He concludes that blues he generally sees the same as other people and purple is just a little bit different from blue. He described brown in the same creative way that he does other colors, writing, quote, my idea of brown I obtained from a piece of white paper heated almost to ignition.

[Holly Fry]

He also notes that seeing colors in moonlight presents the same or near same results for him as seeing them in candlelight. Lightning gives the same effect as daylight. It doesn't matter whether the sun is rising or setting when it comes to color, and any kind of combustible substance creates the same color perception as any other flame. He concludes this section of the paper with quote, my vision has always been as it is now.

[Tracy V. Wilson]

His next section breaks out the information that he's collected from other people and their Perceptions of color, starting with people he has found who have vision that seems similar to his own.

[Holly Fry]

And Dalton mentions Mr. Harris of Maryport and his alternate perceptions of color. Dalton thought that based on the description, Harris's anomalous vision might have been different from his own. He discovered that one of Harris's brothers was still alive, so he made contact and went to visit. Upon questioning this brother and testing his vision, Dalton found that the Harris family seemed to have the same genetic variable that he and his brother had when it came to how they perceived the colors of the world around them.

[Tracy V. Wilson]

This led to a general line of questioning of the students and colleagues that Dalton regularly came in contact with, kind of as a subject group. And he found a small proportion of them shared his specific experience regarding pink and light blue, looking similar by daylight and different by candlelight. Dalton also found just a couple of examples of people who, quote, differ from the generality and from us also, meaning that they seem to have a different type of color vision deficiency. He also mentioned a shared experience among all of these people that just as with him, it had not occurred to them that they were seeing things differently from the majority of people, but that they too found the names and groupings of colors perplexing at times.

[Holly Fry]

Though his paper was really the beginning of science's study of color vision deficiency, Even in his really relatively small data set, Dalton was already capturing information that showed a difference in instances of color vision deficiency in regards to people's sex. He noted that in the Harris family, four of six sons in the family had what would come to be known as color vision deficiency, sometimes also called daltonism for obvious reasons, but their sister didn't. Similarly, Dalton and his brother Jonathan had the same color experience, but their sister did not. He wrote, quote, it is remarkable that I have not heard of one female subject to this peculiarity.

[Tracy V. Wilson]

He also included the line, quote, I did not find that the parents or children in any of these instances have been so, unless in one case. So even though he didn't really realize it, he was gathering information on the recessive genetic nature of red green color vision deficiency.

[Holly Fry]

Next up, we'll talk about what Dalton thought was causing his anomalous vision. But first, we will take a break for a word from our sponsors.

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[Tracy V. Wilson]

The third section of Dalton's paper tries to unravel the cause of what he was referring to as, quote, our anomalous vision. One of the ways that he worked out his theory here was to work with transparent colored liquids, and then he would have various people look at objects through those transparent colored liquids to record their perception of color. So he would hold up a thing behind like a tank of blue water, whatever, and ask them what they saw. And because people with, you know, quote, unquote normal vision described color similar to what he saw in his normal day to day life when they looked through a tank of blue water, he came to this incorrect conclusion that, quote, one of the humors of my eye must be a transparent but colored medium so constituted as to absorb red and green rays, principally because I obtain no proper idea of these in the solar spectrum and to transmit blue and other colors more perfectly.

[Holly Fry]

Honestly, this is a totally reasonable conclusion based on understanding it right? He outlined how this would impact the perception of various colors and then addressed why the colors changed so drastically for him and others like him in Candlelight Riding Queen quote, when any kind of light is less abundant in blue, as is the case with candlelight compared to daylight, our eyes serve in some degree to temper that light so as to reduce it nearly to the common standard. The Earth's atmosphere, he believed, was a blue fluid that modifies the sun's light so as to occasion the commonly perceived difference.

[Tracy V. Wilson]

So this paper was met with some curiosity, and his very detailed comparisons of his vision to that of other people who saw color normally offered a lot of insights. But this idea of a blue humor in his eye that was causing his anomalous color vision was kind of dismissed by the scientific community. And in response, Dalton, who really thought he was onto something with it, donated his eyes to science. He wrote up a document that requested that his eyes be dissected upon his death to see if he had been correct and whether there was any other physical evidence to explain the way he perceived color.

[Holly Fry]

A little less than a decade after Dalton's writing on his anomalous vision scientist Thomas Young published On the theory of light and colors. And this put forth the idea that there were receptors in the eye for each of the colors red, green and blue. So he was totally onto it. And Young addressed Dalton's work and his anomalous color vision with a different theory that there was a, quote, absence or paralysis of those fibers of the retina which are calculated to perceive. He was so completely on the right track that you would think that this would have just broken eye science wide open. But no, no, it advancement slowed down after this in studying the eye, and that went on for decades.

[Tracy V. Wilson]

Yeah, it was like people were like, neat idea. And they moved on to other stuff beyond the study of color vision deficiency. John Dalton, of course, continued to make important contributions to the scientific world. Concurrently, while working on figuring out why he couldn't see flowers the same way as other people, he also published a work titled Meteorological Observation and Essays. He published additional work in meteorology as well. And his work in this field led to some fellow scientists considering him the father of meteorology. Although his work. Anytime somebody gets called the father of something, I always have to go, eh? Because his work was of course, building on that of his mentors on the subject. He had particularly had a really good mentor in meteorology when he was studying as a teacher.

[Holly Fry]

Dalton also did a lot of work in chemistry, specifically atomic theory. His work in this area came to some incorrect conclusions, but it was also instrumental in moving the scientific community away from the long held idea that matter was at the basic level, all the same and just configured differently to form different things. Things.

[Tracy V. Wilson]

Dalton championed the idea that there were all kinds of different atoms with different sizes and weights and that they behaved differently. He started a project to measure the masses of different atomic particles to begin cataloging all of the different atoms that could be found. He presented the first table of atomic weights in 1803, and his work in this area propelled organic chemistry forward. He is also sometimes called the father of chemistry.

[Holly Fry]

Dalton had joined the Manchester Literary and philosophical Society in 1793, when he was still in his 20s. In 1817, as a man in his early 50s, he became its president. Though he held this position for the rest of his life, his scientific career slowed down quite a bit.

[Tracy V. Wilson]

Yeah, there were some other issues where his. He had some papers that were denied for publication, and it just wasn't like the. The heyday he had had when he was a little younger. He had the unique distinction, though, of seeing, for example, his own statue erected in Manchester during his lifetime for his accomplishments. And while he had been barred from an education at Oxford or Cambridge as a young man because he was a Quaker, not an Anglican, he received honorary degrees from both. Later in life, he also served as a foreign associate of the French Academy of Sciences.

[Holly Fry]

On April 18, 1837, Dalton, who was 70 at the time, had a stroke that resulted in a partial paralysis. And then he had another small stroke or possibly a seizure several days later. Being pretty pragmatic, he set his affairs in order as soon as he was recovered enough to do so. But then he lived another seven years. He continued as president of the Literary and Philosophical Society. He made visits to lake country. That's something that he had been doing throughout his life.

[Tracy V. Wilson]

Yeah, it was a very close call. And then he kind of was like, well, I'm still alive. I'm gonna keep doing my living stuff. John Dalton died finally on July 27, 1844. He was really, really beloved in Manchester by this point, and he was given a public funeral by the city on August 12, 1844. An estimated 40,000 people paid their respects before Dalton was interred.

[Holly Fry]

The day after Dalton's death on July 28, 1844, his wishes were carried out. Out. His eyes were dissected. This was done by Dr. Joseph Ransom to determine whether this idea about having a blue humor in his eye was correct. Of course, it was not. Ransom described what he found in Dalton's eye as, quote, perfectly pellucid. Ransom also sliced off a section of the posterior pole of the eye and used it as a lens to see if colors that were viewed through it, especially red and green, took on a different hue, which they did not.

[Tracy V. Wilson]

But Dalton's eyes were not discarded after that. So for clarity, he did the full dissection on one eye. That little part he sliced off was from the second eye. So he had only taken the primary samples from one. The other was mostly intact. And the remains of Dalton's eyes were preserved and were eventually given to the Manchester Literary and Philosophical Society. That was not the end of their story. A hundred years after Dalton died in 1995, a DNA analysis was conducted on his preserved eye eyes. And this examination determined that he had deuteronopia, conclusively proving that he had red green color vision deficiency.

[Holly Fry]

Two years after those findings were published in 1997, the eyes were donated to the Science and Industry Museum in Manchester. They remain in the collection there to this day.

[Tracy V. Wilson]

Yep, you can find pictures of them online. In the 1870s, German anatomist Max Schultz identified the rods and cones of the retina and deduced that rods were dedicated to night vision and cones to daylight light vision. Then later in the 1870s, Wilhelm Kuhn laid the groundwork for a concept of photochemical basis for vision.

[Holly Fry]

In the 1890s, Spanish neuroscientist Santiago Ramon y Cajal studied the retina and drew detailed diagrams of the cells within it. Cajal's scientific drawings are incredibly intricate and very beautiful and they were part of an art exhibit at NYU in 2018.

[Tracy V. Wilson]

Yeah, so you know, all of the things that would have explained to Dalton what was going on came a little too late. There was also a cool discovery in 1991. So fairly recently a new kind of photoreceptor was discovered, the ganglion cell, and that once again refined our knowledge of how the human eye takes in and processes visual information. Always learn. I really really really love John Dalton's story and I love this part of it. I knew a little bit more about his work in establishing the basis of a lot of the chemistry we use, but I didn't. I had never read this paper before and I honestly it's the most fun reading.

[Holly Fry]

Thanks so much for joining us on this Saturday. If you'd like to send us a note, our email address is historypodcastiheartradio.com and you can subscribe to the show on the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.

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[Holly Fry]

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[Tracy V. Wilson]

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