Mary Parsons (née Field), Countess of Rosse, Anglo-Irish amateur astronomer, architect, furniture designer, and pioneering photographer, is born on April 14, 1813, at Heaton Hall, Heaton, Bradford, West Yorkshire, England. Often known simply as Mary Rosse, she is one of the early practitioners of making photographs from waxed-paper negatives.

Field is the daughter of John Wilmer Field, a wealthy estate owner. She has a sister, Delia, and they are educated at home by Susan Lawson, a governess who encourages her creativity and broad interests, including astronomy. The sisters are joint heirs to their father’s fortune.

Through her family Field meets William Parsons, then Lord Oxmantown and the future 3rd Earl of Rosse, an Anglo-Irish astronomer and naturalist, and they are married on April 14, 1836, her 23rd birthday. In February 1841, Lord Oxmantown succeeds his father in the family peerage to become the 3rd Earl of Rosse. She, Baroness Oxmantown since her marriage, thus now becomes the Countess of Rosse.

In the early 1840s the couple becomes interested in astronomy, and the Countess of Rosse helps her husband build a number of giant telescopes, including the so-called Leviathan of Parsonstown, that is considered a technical marvel in its time. The author, Henrietta Heald, contends that she is not only a financial support to the building of the telescope, but is also involved in a practical and intellectual capacity. The Leviathan of Parsontown is completed in 1845 and holds the record as the world’s largest telescope for over 70 years. It is mentioned in Jules Verne’s science fiction novel, From the Earth to the Moon.

The Countess of Rosse is an accomplished blacksmith, which is very unusual for higher class women of the time, and she may have constructed some of the iron work that supports the telescope. Other metal cast items around the castle grounds are designed by her, including bronze gates.

During the Great Famine of 1845–47 in Ireland, the Countess of Rosse is responsible for keeping over five hundred men employed in work in and around Birr Castle, where she and her husband live.

The Countess of Rosse creates a huge dining room at Birr Castle in which to entertain scientific guests, which becomes increasingly used when Lord Rosse becomes President of the Royal Society of London in 1848. Guests include mathematician William Rowan Hamilton, who writes her a sonnet about his experience of gazing through the Leviathan.

In 1842, Lord Rosse begins experimenting in daguerreotype photography, possibly learning some of the art from his acquaintance William Henry Fox Talbot. In 1854, he writes to Fox Talbot saying that the Countess too has just commenced photography and sends some examples of her work. Fox Talbot replies that some of her photographs of the telescope “are all that can be desired.”

The Countess of Rosse becomes a member of the Dublin Photographic Society, and in 1859 she receives a silver medal for “best paper negative” from the Photographic Society of Ireland. Many examples of her photography are in the Birr Castle Archives. Much of the topography of Birr Castle that she portrayed has changed very little, and it is possible to compare many of her photographs with the actual places. She records the Leviathan in her photographs including one image showing her three sons, Clere, Randal and Charles along with her sister-in-law, Jane Knox, standing upright at the mouth of the telescope.

The Countess of Rosse gives birth to eleven children, but only four survive to adulthood:

• Lawrence Parsons, 4th Earl of Rosse (1840–1908)
• Reverend Randal Parsons (1848–1936)
• Hon. Richard Clere Parsons (1851–1923), apparently made a name for himself building railways in South America.
• Sir Charles Algernon Parsons (1854–1931), known for his commercial development of the steam turbine. His wife, Lady Katharine Parsons and their daughter Rachel Parsons are founders of the Women’s Engineering Society and its first and second presidents.

Mary, Dowager Countess of Rosse, dies in 1885.