(b. Portsea, England, 28 April 1854; d. New Cottage, North Lancing, Sussex, England. 26 August 1923)
Ayrton, born Phoebe Sarah Marks, was the third of six children of Levi and Alice Theresa (Moss) Marks. Her father, a Polish-born clockmaker and jeweler, died in 1861 leaving the family in debt. Sarah received her early education through the beneficence of an aunt. While she was in her teens she adopted the name Hertha, after the Teutonic goddess eulogized by Swinburne in a popular poem. From the age of sixteen she considered herself an agnostic, but she always remained proud of her Jewish heritage.
Hertha Marks first supported herself by tutoring and embroidery work, sending much of her earnings to her impoverished family. Her dream of a university education was made financially possible largely through the efforts of Barbara Leigh-Smith Bodichon, one of the founders of Girton College, Cambridge. Hertha entered Girton in 1876 after having passed the Cambridge University Examination for Women in 1874 with honors in English and mathematics. She was coached by Richard T. Glazebrook and completed the Cambridge Tripos in 1881. At that time women could not receive a Cambridge degree.
Marks’s invention and patenting of a line divider in 1884 led her to consider a scientific career. She began studies that year at Finsbury Technical College. London, under the professor of physics and noted electrical engineer William Edward Ayrton. They were married on 6 May 1885.
After the birth of their daughter Barbara, Ayrton began experiments with the electric arc, at first assisting her husband but soon taking over the researche completely.
In 1893 the direct-current are was widely used for lighting, and was therefore of significant commercial and industrial interest. Arc lamps were plagued with problems. They hissed, sputtered, hummed, and rotated, producing unsteady illumination in a changing array of colors. Their heat melted most materials, a challenge for those who wished to devise suitable insulators. Since the are electrodes were consumed during operation, the are length continually changed, which required adjustments to be made in the circuit. It could be difficult to maintain the are light, particularly with long arcs or low currents. The functional dependence of potential on time and position within the are and the way are resistance varied were all unknown. Scientists had debated the merits of various types of carbon electrodes but had reached no consensus to guide the manufacturers.
Ayrton investigated the relations in the directcurrent are between power supplied, potential across the arc, current, and are length, Her results, which she showed agreed with data of other observers, were that (I) power used in the are is a linear function of the current when are length is held constant; (2) power is a linear function of are length when current is held constant; (3) potential and current are inversely proportional when are length is held constant. These results (for solid carbons and silent arcs) can be expressed by the equation V = a + bl + (c + dl)/A, where V is the potential difference between (lie electrodes, l is the arc length, A is the current, and a, b, c, and d are constants that depend on the electrodes.
Ayrton next showed that the potential required to send a given current through a fixed are length depends principally upon the nature of the surface of the depression (crater) that forms on the tip of the positive carbon (or is performed during manufacture). By casting the are image onto a screen, she was able to describe and explain both the arc’s appearance and the changes that occurred in the carbons during operation.
Ayrton’s tour de force was her analysis of the hissing arc, the instability of which presented a baffling engineering problem. She found that this undesirable condition resulted from oxidation of the positive carbon. (In the stable are only vaporization of the carbon took place.) The proximate cause of hissing was the positive crater’s spread from the tip of the carbon to its sides. Theresulting fissure allowed air to rush into the arc. causing the light to rotate and producing a noise similar to that created by wind blowing through a door frame. Obviously the then-common practice of manufacturing carbons with grooves along their sides led to the very condition the engineer wished to avoid, Moreover, electrodes with flat ends would be able to withstand higher currents than the usual tapered carbons before they developed grooves.
This paper established Ayrton’s reputation, and in 1899 the Institution of Electrical Engineers permitted her to read the paper herself (which was unusual for a woman) and awarded her £10 for it. In May 1899 she was elected the first woman member.
In 1902 Ayrton published The Electric Arc, a comprehensive study based mainly on her published papers and including a useful historical survey. In the book she also showed that the common assumption by engineers of a large “back E.M.F.” or a negative resistance in the are was not necessary, and that short arcs were more efficient than long arcs.
Ayrton patented a number of improvements in searchlight carbons that she developed for the British Admiralty. She also designed improved cinema projectors.
During 1901, while she cared for her ailing husband at the shore, Ayrton analyzed sand ripple patterns formed on the beach by the sea. She showed that a succession of water vortices originated from each ripple in turn, thus creating the patterns. These studies found a practical application in the Ayrton fan, a hand-operated device she designed during World War 1 to clear poisonous gases from the trenches by means of air vortices. A variety of hindrances prevented the fan from being widely used, a failure that pained her deeply.
In 1906 the Royal Society awarded Ayrton the Hughes Medal for her experimental investigations of the electric arc, and also for her work on sand ripples. In spite of this and other honors (she apparently was the first woman to read her own paper to the Royal Society, in 1904), the society declined to elect her a fellow, deciding that, as a married woman, she was not qualified for election.
Ayrton and Marie Curie met in 1903 and were friends until Ayrton’s death. During 1912 Ayrton provided a refuge for Curie and her daughters, enabling the famous physicist to recuperate anonymously from stress and illness.
For much of her life Ayrton was plagued by ill health. She nevertheless was active in charitable causes and especially in the suffrage movement. She left the considerable sum of £8, 160 to the Institution of Electrical Engineers (The Electrician. 91 , 469), the organization that had welcomed her without prejudice and helped launch her career.
I. Original Works. Ayrton’s most important work is The Electric Arc (London, 1902), which contains references to most of her earlier papers on the arc. Other significant papers are “The Uses of a Line-Divider,” in Philosophical Magazine, 19 (1885), 280–285 (by Sarah Marks); “The Mechanism of the Electric Arc,” in Philosophical Transactions of the Royal Society of London, A 199 (1902), 299–336: “On the Non-periodic or Residual Motion of Water Moving in Stationary Waves,” in Proceedings of the Royal Society of London. A80 (1908), 252–260: “The Origin and Growth of Ripple-Marks,” ibid., 84 (1910). 285–310, (read 1904); “Local Differences of Pressure near an Obstacle in Oscillating Water.” ibid., 91 (1915), 405–510; and “On a New Method of Driving off Poisonous Gases,” ibid., 96 (1919–1920). 249–256.
II Secondary Literature. A biography is Evelyn Sharp, Hertha Ayrton. 1854–1923 (London, 1926). See also the unsigned “Mrs. Ayrton,” in The Electrician, 91 (1923), 211 227; Henry Armstrong, obituary in Nature, 112 (1923), 800–801, with a response by T. Mather. ibid., 939; the article on Ayrton in Marilyn Bailey Ogilvie, Women in Science (Cambridge, Mass., 1986); and A. P. Trotter, “Mrs. Ayrton’s work on the Electric Arc,” in Nature, 113 (1924), 48–49.