Phoebe Sarah Hertha Ayrton (28 April 1854 – 26 August 1923[1]) was a British electrical engineer, mathematician, physicist and inventor, and suffragette.

She also constructed a sphygmomanometer (blood pressure meter), led the choral society, founded the Girton fire brigade, and, together with Charlotte Scott, formed a mathematical club.

She adopted the name "Hertha", first given as a nickname by her friend Ottilie Blind, after the eponymous heroine of a poem by Algernon Charles Swinburne that criticised organised religion.

[8][9] Upon her return to London, Ayrton earned money by teaching and embroidery, ran a club for working girls, and cared for her invalid sister.

In 1884 Ayrton patented[10] a line-divider, an engineering drawing instrument for dividing a line into any number of equal parts and for enlarging and reducing figures.

In 1895, Hertha Ayrton wrote a series of articles for the Electrician, explaining that these phenomena were the result of oxygen coming into contact with the carbon rods used to create the arc.

[1] She petitioned to present a paper before the Royal Society but was not allowed because of her sex and "The Mechanism of the Electric Arc" was read by John Perry in her stead in 1901.

[4] Ayrton was also the first woman to win a prize from the Society, the Hughes Medal, awarded to her in 1906 in honour of her research on the motion of ripples in sand and water and her work on the electric arc.

[3] By the late nineteenth century, Ayrton's work in the field of electrical engineering was recognised more widely, domestically and internationally.

In a history of housework in the British Isles, Caroline Davidson called Ayrton one of the rare "female electrophiles" who contributed to the advancement of electricity in ways that transformed women's labor within homes.

"[7] She was the fifth recipient of this prize, awarded annually since 1902, in recognition of an original discovery in the physical sciences, particularly electricity and magnetism or their applications, and as of 2018, one of only two women so honoured,[7] the other being Michele Dougherty in 2008.

[16] As a teenager, Ayrton became deeply involved in the women's suffrage movement, joining the WSPU in 1907 after attending a celebration with released prisoners.

In 1909 Ayrton opened the second day of the Knightsbridge "Women's Exhibition and Sale of Work in the Colours" which included new model bicycles painted in purple, white and green and raised from 50 stalls and tea etc.

[17] Ayrton was with the delegation that went with Emily Pankhurst to see the Prime Minister and met his private secretary instead on 18 November 1910 (Black Friday).

[14] Although Curie usually chose to withhold her name from petitions, Ayrton managed to persuade her to sign a protest against the imprisonment of suffragettes through her daughter[clarification needed].

The invention was dismissed by the War Office initially, until press exchanges followed, and they finally issued 104,000 “Ayrton Fans” to soldiers on the western front.