Figure 1: John Ray Figure 2: Henrietta Swan Leavitt
Who are they? How many people would be able to name the two scientists pictured above? History seems to have forgotten them. Each one is of great importance in their fields of expertise, but relatively unknown nowadays to most people outside science.
Both Ray and Leavitt were overshadowed by scientists who were working around the same time or after them. Linnaeus is more familiar than Ray because he was vocal about his achievements and confident about presenting them to the public. Leavitt is relatively unknown because of the extraordinary achievements of Hubble shortly after (similarly to Rosalind Franklin and Crick and Watson).
This article will give a brief overview of their lives and most significant achievements and will explore the legacy of their work on our scientific knowledge today.
John Ray (1627-1705)
“John Ray is a name most people have never heard of. Yet for me, he is one of the greatest naturalists ever.” (Timothy Walker, lecturer in Biological Sciences at Oxford University) 
Figure 3: The Scientist Window in Trinity College Chapel
Figure 4: Detail of the John Ray stained glass in Trinity College Chapel
John Ray was an English naturalist who wrote about Botany, Zoology and Natural Theology (the practice of trying to prove the existence of God by looking at the natural world). He went to Cambridge University aged sixteen, where he later lectured in Greek, Maths and Humanities. Because of his Puritan beliefs, he refused to swear an oath of allegiance to Charles II, which led to him leaving Cambridge.
With his student Francis Willughby, Ray travelled through England and Wales looking for birds and plants to classify. Although most of Willughby’s works have been lost, both his and Ray’s books and ideas were used by Carl Linnaeus to write his Systema Naturae (1735). In fact, Willughby is yet another forgotten scientist who became important in his own right.
In 1662, Willughby and Ray decided to try to observe all species with the aim of classifying them. This was something that had not been done before, and they felt that the existing literature and system of naming were unclear. They started by classifying British species before then going onto species in Europe. For example, they looked at the shape of the bird’s beak to help create a branching classification of land and waterfowl. They did this more than a century before Darwin did the same thing on the Galapagos. The taxonomy (a classification system) which they developed would be used extensively by naturalists in the eighteenth century. Classification is important across the sciences because without it it would be difficult to group things logically and systematically. This method of categorization, which eventually became Linnaeus’ binomial system, is as fundamental to biologists as Mendeleev’s Periodic Table is to chemists, and the Messier catalogue of deep-sky objects is to astronomers. The International Institute for Species Exploration (IISE) relies on this internationally accepted taxonomy system to order new species and to understand the connections among them.
“Classification and name-giving will be the foundation of our science.” (Carl Linnaeus, Systema Naturae, 1735) 
Ray and Willughby travelled through Europe mostly on horse or mule, and after a difficult crossing of the Alps reached Venice. There, they spent three months dissecting and drawing fish from the fish market. They observed and measured the external features of their specimens. They wanted to find a unique feature that connected the specimen with others of the same species, and which separated it from those of different species. Willughby called this a “distinguishing mark”.
“Thus, no matter what variations occur in the individuals or the species, if they spring from the seed of one and the same plant, they are accidental variations and not such as to distinguish a species.” (John Ray, History of Plants) 
Ray and Willughby later lived in Middleton Hall, the home of the Willughby family. Ray collected plants, took them home, and examined them closely. He saw patterns that had not been identified by other botanists and realised that different plants come from the seed of the same plant. (He saw that a bean seed cuts easily into two, while an iris seed has just one structure in the middle). Timothy Walker in his documentary Botany, a blooming history says that “this moved the study of plants away from superstition towards science”. (The study of plants was originally associated with traditional beliefs and ideas involving herbalism). Ray identified and named monocots and dicots: monocots are flowering plants that only contain one seed leaf inside the seed coat, while dicots have two. This is a fundamental division which remains important today; in fact, his principles of classification, which he formed by looking at the whole plant, are still taught to this day. Ray was also one of the first people to use dendrochronology to explain how to find the age of a tree from its rings. When Willughby died, Ray edited his book called The Ornithology of Francis Willughby. He later moved to Black Notley in Essex where he spent the rest of his life. He continued to work and write books until he died.
Figures 5 and 6: From ‘The Ornithology of Francis Willughby’
Ray did not achieve much acknowledgement in his lifetime, for several reasons. He wrote in Latin (which most normal people could not read at the time), he could not afford illustrations (which made his books very dense) and he was very humble (compared to Linnaeus, who called himself the Prince of Botany.) In the preface to The Wisdom of God he describes his book as an “inconsiderable trifle”, and in each book he apologises to the readers for putting them to the trouble of reading it. Nonetheless, his definition of a species was a major breakthrough in the biological classification of plants.
Figure 7: Title page from ‘The Wisdom of God’
Figure 8: Title page from ‘The History of Plants’
Henrietta Swan Leavitt (1868-1921)
Henrietta Swan Leavitt was an American astronomer. She studied at Harvard University (later Radcliffe College), Cambridge, Massachusetts. She began by studying a mixture of subjects including Classical Greek, Calculus and Philosophy and only started Astronomy in her fourth year.  After graduating she became ill and as a result of this illness she suffered from deafness for the rest of her life.
“I should be willing to pay thirty cents an hour in view of the quality of your work, although our usual price, in such cases, is twenty five cents an hour.” (Edward C Pickering) 
Leavitt worked as a “computer” at the Harvard College Observatory. The computers were a group of women who were employed to examine photographic plates which had been gathered from different telescopes. The photographs were taken by the men and the women were tasked with assessing the plates and the brightness of the stars. The women were not allowed to do much theoretical work or to operate the telescopes. Henrietta joined as an unpaid volunteer, but she eventually became head of the photographic department. Her job was to classify Cepheid variable stars (those that vary in brightness). She noticed a pattern: the brighter the star, the larger the period of fluctuations. Figure 9 below shows how the changes in the star’s size causes fluctuations in its luminosity or absolute magnitude (a star’s true brightness).
Figure 9: Cepheid Variable Star Graph
The period of a star is the time it takes for it to return to the same point in its orbit. By measuring the period of the star, its luminosity could be found, which along with its apparent magnitude (the brightness of a star as seen from Earth), could be used to determine the distance to the star. This meant there was a relationship between the period of the stars and their apparent magnitudes. Leavitt knew that these Cepheid Variable stars were the same distance from Earth so any variations in their apparent magnitudes must be due to the difference in their absolute magnitudes. Henrietta’s discovery was important because it meant that the Cepheid stars could be used as ‘standard candles’: objects of known luminosity that can be used to measure distances to interstellar objects. Leavitt discovered 1,777 variable stars in the Magellanic Clouds.
Figure 10: Large Magellanic Cloud
This discovery allowed astronomers to calculate the relative distance to stars. They could not calculate the absolute distance as there was no accurate information about the distances to the Large and Small Magellanic Cloud, which is where the Cepheid stars that Leavitt was looking at are found. The Danish astronomer Ejnar Hertzsprung (1873-1967) realized that to calculate absolute distances he needed to accurately measure both the distances and the absolute magnitudes of a number of Cepheid variables. He later developed the Hertzsprung-Russell diagram, which is one of the most important diagrams in astronomy. It shows the relationship between the temperatures of stars and their absolute magnitudes.
Figure 11: Hertzsprung-Russell Diagram
Edwin Hubble used Leavitt’s discovery, along with the findings of Vesto Slipher (1875-1969), who discovered red shift, to work out the absolute distance to stars and, eventually, the size of the universe. Red shift is an increase in wavelength which enables astronomers to calculate the speed at which an object is moving away from us on Earth. As most galaxies are red shifted, this tells us that the universe is expanding. Hubble used Leavitt’s laws to gather “the first observational evidence for the Big Bang”. Her work prompted Hubble to suggest that the Milky Way is not at the centre of the universe by using her method of Cepheid Variables as benchmarks for calculating distances in space. This enabled Hubble to prove that the universe extended far beyond our own galaxy. Another astronomer, Harlow Shapley, also used her ideas as a basis for repositioning the Sun away from the centre of the galaxy. Leavitt’s discovery is vital to modern cosmology, but she never knew the impact of it. It was only posthumously that an asteroid and a crater on the Moon were named in her honour. Knowing who Leavitt was and what she did makes modern research in astronomy more understandable.
One of the reasons the Hubble Space Telescope (which is actually an observatory based in space) was set up, was to help calculate the age of the universe. It allowed astronomers to do this by measuring the brightness of dozens of Cepheid variables and “from this study and other related analyses, astronomers determined the Hubble constant and the universe’s age to an accuracy of about 5 percent.” (Hubblesite, 2010 )
Research published in April 2019 on the Hubblesite describes how astronomers are building on Leavitt’s work to enable them to better understand how the universe is expanding, and how her discoveries provided the foundation for much of what the Hubble Telescope has been able to do. “In this new study, astronomers used Hubble to observe 70 pulsating stars called Cepheid variables in the Large Magellanic Cloud. The observations helped the astronomers “rebuild” the distance ladder by improving the comparison between those Cepheids and their more distant cousins in the galactic hosts of supernovas”. (Hubblesite, 2019) 
Figure 12: Hubble Telescope
Even though Hubble did suggest that Leavitt should receive the Nobel Prize for her work, others say that both he and Shapley were less generous toward her: “Hubble’s underwhelming acknowledgment of Leavitt is an example of the ongoing denial and lack of professional and public recognition that she suffers from, despite her landmark discovery.” (Pangratios Papacosta, Science Historian, The Astronomy Book, 2017, 137)
Indeed, when Leavitt was nominated for the Nobel Prize the mathematician who nominated her did not know that she had been dead for four years. She never received the Nobel Prize, and Shapley suggested that the credit was his for interpreting her data.
Both Leavitt and Ray noticed patterns that nobody had seen before. These observations led to future discoveries, because patterns impose order and structure, allowing different ideas to be connected. Patterns help theories to be developed and reliably tested. Scientists from various disciplines have always searched for patterns and they surround us in nature: in the shell of the nautilus, the spirals of sunflower seeds, the murmuration of starlings and the arrangement of a shoal of fish. The patterns that Ray noticed enabled plants to be classified into different species in a logical way. Leavitt’s patterns in the stars laid the foundations for later calculations of the size and age of the Universe.
“As my teacher revealed to me all those years ago, a mathematician is a pattern searcher. I try to find the logic or the pattern that helps to generate the world I see around me”. (Marcus du Sautoy, Finding Moonshine, 2007, 96)
Figure 13: Sunflower Seeds Figure 14: Starling Murmuration
Ray and Leavitt were both disadvantaged, although in different ways, by the society in which they lived. Leavitt was limited in what she was allowed to do, because of the attitudes towards women at the time. Although there were colleges for women in America, the sciences were still dominated by men. Not only was she paid less than the men, but she and the other women were only allowed to do what was considered boring and tedious work. Opportunities for women in science were often limited to helping the men. Caroline Herschel, for example, was the first woman to discover a comet, and later went on to discover three nebulae. Nevertheless, she was seen only as an assistant to her brother, William Herschel. The only work Leavitt was allowed to do was to sort and categorize the collection of photographic plates with images of the night sky, and to calculate the images they showed of the stars. But the logbooks and the photographic plates she used are still kept at the Harvard Smithsonian Center for Astrophysics.
“(They) constitute a perfect record of what the night sky looked like a century ago, and of the women who sat in the small room next to Harvard’s telescope, deciphering the secrets of the universe.” (Zing Tsjeng, Forgotten Women: The Scientists, 2018, 17) 
Ray’s Protestant beliefs prevented him from continuing his academic career at Cambridge. This meant that he never became as famous as others who stayed at their universities and developed their ideas, such as Christopher Wren and Isaac Newton. He was the son of a blacksmith and remained relatively poor all his life, relying on the financial support of friends to enable him to pursue his career. All of these circumstances mean that both he and Leavitt remain forgotten scientists.
1. “Botany: A Blooming History,” YouTube video, 58:59, “Documentary – Natural World” January 5, 2015. Accessed June 30, 2019.
2. John Ray, Wikipedia. Accessed June 30, 2019.
3. Elizabeth Yale. 2018. “The Forgotten Founder of Ornithology.” Nature, May 2, 2018. https://www.nature.com/articles/d41586-018-05011-5
4. Carl Linnaeus, Systema Naturae. Netherlands, 1735. Accessed July 9, 2019. https://todayinsci.com/L/Linnaeus_Carolus/LinnaeusCarolus-Quotations.htm
5. Simon Worrall, 2018. “The Amazing Tale of the Genius that History Forgot” National Geographic, August 17, 2018. https://www.nationalgeographic.com/science/2018/08/genius-naturalist-willughby-evolution/
6. John Ray, The wisdom of God manifested in the works of the Creation. London: W and J Innys, 1743. Accessed 7 July, 2019 https://books.google.es/books?id=dxkHAAAAQAAJ&printsec=frontcover&redir_esc=y#v=onepage&q&f=false
7. Jacqueline Mitton(ed.), Robert Dinwiddie, David W. Hughes, Tom Jackson, and Penny Johnson. The Astronomy Book: Big Ideas Simply Explained. London: DK, Penguin Random House, 2017.
8. “Henrietta Leavitt.”History of Scientific Women. Accessed July 8, 2019. https://scientificwomen.net/women/leavitt-henrietta-55
9. “Hubblecast 116: Henrietta Leavitt- ahead of her time,” YouTube video, 4:13, “HubbleESA,” February 20, 2019. Accessed July 9, 2019.
10. Mario Livio, “Starry-eyed Hubble Celebrates 20 years of Awe and Discovery,” Hubblesite, April 22, 2010. Accessed July 10, 2019. https://hubblesite.org/contents/news-releases/2010/news-2010-13.html
11. Adam Riess, “Mystery of the Universe’s Expansion Rate Widens with new Hubble Data,” Hubblesite, April 25, 2019. Accessed 10 July, 2019. https://hubblesite.org/contents/news-releases/2019/news-2019-25.html?Topic=104-stars-and-nebulas
12. Marcus Du Sautoy, Finding Moonshine. London: Harper Collins, 2009.
13. Zing Tsjeng, Forgotten Women: The Scientists. London: Cassell Illustrated, 2018.
Fig 1. Unknown Artist, John Ray, date unknown, oil on canvas, 30×26 in., National Portrait Gallery. Accessed June 30, 2019. https://en.wikipedia.org/wiki/John_Ray
Fig 2. Photo of Henrietta Swan Leavitt, date and author unknown. Accessed July 8, 2019. https://en.wikipedia.org/wiki/Henrietta_Swan_Leavitt
Fig 3. Jennifer Brown, The Scientist Window in Trinity College Chapel, date unknown. Accessed July 10, 2019. https://www.braintreemuseum.co.uk/john-ray-archive-at-the-university-of-cambridge/
Fig 4. Jennifer Brown, Detail of the John Ray Stained Glass in Trinity College Chapel, date unknown. Accessed July 9, 2019. https://www.braintreemuseum.co.uk/john-ray-archive-at-the-university-of-cambridge/
Fig 5. Francis Willughby, Illustration, Ornithology, 1676. Accessed July 9, 2019. https://www.donaldheald.com/pages/books/32389/francis-willughby-john-ray/the-ornithology-of-francis-willughby-in-three-books-wherein-all-the-birds-hitherto-known-are
Fig 6. Francis Willughby, Illustration, Ornithology, 1676. Accessed July 9, 2019. https://www.donaldheald.com/pages/books/32389/francis-willughby-john-ray/the-ornithology-of-francis-willughby-in-three-books-wherein-all-the-birds-hitherto-known-are
Fig 7. John Ray, Title Page from The Wisdom of God, 1743. Accessed July 7, 2019. https://archive.org/details/wisdomofgodmanif00ray/page/n3
Fig 8. John Ray, Title Page from Historia Plantarum, 1686. Accessed July 7, 2019. https://en.wikipedia.org/wiki/Historia_Plantarum_(Ray)
Fig 9. Courtney Seligman, Diagram of variation in brightness and size of a typical Cepheid Variable, date unknown. Accessed July 6, 2019. https://cseligman.com/text/stars/variables.htm
Fig 10. Eckhard Slawick, Large Magellanic Cloud, photo, 2018. Accessed July 5, 2019. https://earthsky.org/clusters-nebulae-galaxies/the-large-magellanic-cloud
Fig 11. Stefan V, Hertzsprung-Russell diagram, 2016. Accessed July 1, 2019. https://socratic.org/questions/what-is-the-hertzsprung-russell-diagram-and-why-is-it-so-important-to-astronomy-
Fig 12. Media Fusion Inc, Hubble Telescope, photo, 2005. Accessed July 2, 2019. https://www.turbosquid.com/3d-models/3d-hubble-telescope-satellite-model/254617
Fig 13. Luca Postpischi, Flickr, Sunflower, photo, 2015. Accessed July 4, 2019. http://thesmarthappyproject.com/fibonacci-in-a-sunflower/
Fig 14. Accessed July 4, 2019. https://www.attenboroughnaturecentre.co.uk/things-to-see-and-do/starlings
About the Author
Caleac lives in Spain and is home educated. She enjoys all STEM subjects especially Astronomy and Biology. She has a Diploma in Classical Guitar and qualifications in Latin, Ancient Greek, Astronomy and Marine Science. She plays tennis at county level. She hopes to study Natural Sciences at university in the future.