I do not think that I met Mrs. Ayrton (Prof. Ayrton's second wife) until about 1895 when she began to contribute articles on the electric arc to The Electrician. Hertha Marks, of Jewish parentage, was one of those women who can pass the Cambridge Little Go after a few months' coaching instead of grinding for years over elementary classics like boys at public schools. She told me that she never regretted the time and trouble of acquiring a smattering of Greek, and agreed that the true object of a 'pass' examination is to discover the capability of acquiring knowledge quite apart from the value of that knowledge. From her youth she had many well-known literary friends.

Hertha Marks was placed equal to First Class in the Little Go, entered Girton, and sat for the Mathematical Tripos. Owing to inadequate coaching she elaborated some questions and left no time for others. It was said at Girton that one of her papers was of higher merit than that of the senior wrangler. But the result was that she took a Third Class. Silvanus Thompson relates in his Memoir of Lord Kelvin how he failed to be Senior Wrangler. It was a case of "bad generalship". In one paper he spent nearly all his time on a particular problem, lost time on it, and there was none left for other questions. Parkinson, the Senior Wrangler in 1845, had not only devoted himself to the art of answering examination questions but had acquired a very rapid handwriting.

Hertha Marks, who had already made the acquaintance of Prof. Ayrton, began to attend his lectures and laboratory in the autumn of 1884, and they were married in the spring of the following year.

During the Chicago Electrical Conference of 1893, a Negro servant lighted a fire with a paper written by Ayrton on "Variation of Potential Difference of the Electric Arc with Current, Size of Carbons, and Distance apart". No rough copy or even an abstract existed of the paper which had not been read in full, and had described an unfinished and inconclusive research. The experiments had been continued by Mrs. Ayrton who sent him her results twice a week by post.

She took up the research and he dropped it, not so much from disinclination to re-write the paper as from a staunch and largehearted wish that the credit for the work should be entirely her own: for Mrs. Ayrton had found that he had been at work on wrong lines. Her results were published in The Electrician and afterwards in book form in 1902. She and I were confrères in the study of the electric arc. I was already familiar with the conditions of her experiments, and we had many talks about them, both in my office as Editor of The Electrician,and at her Kensington Laboratory.

Ayrton had investigated the behaviour of the arc by slowly varying the current between limits for many hours at a time, in fact, often for the greater part of a day. The unhappy arc never had a chance of settling down to adjust itself to any particular current, and looped curves were the result. Mrs. Ayrton, by patient hand control, kept an arc under a steady current for more than an hour at a time, and arrived at a constant definite voltage, or potential difference, as Ayrton called it. She obtained consistent results, expressed them, first in plotted curves, and then as equations, and interpreted the work of previous investigators. Part of the work was on the conditions of the "hissing" arc. In my investigation on the rotating arc I had observed and avoided this stage, and she found that I appreciated her comparison of the handling of the arc to the driving of an obstinate animal after learning its caprices. The references in her book were most kind, and she presented some of my points more correctly and lucidly than I had done. In reply to my letter congratulating her on the publication of her book, and calling attention to a slip, she wrote, "Surely you know that it was a pure accident that your name came just where it did on p.454. I have far too great an admiration for your work on the light of the arc to couple your name with an error which, as you say, you share with so many others... Your experimental comparison of the light of the arc and the area of the crater visible, and your proof of the connection between the two, was a very valuable bit of work, [of] which, I am sure you will allow, I have made the fullest use, and I hope I have clearly expressed my great admiration of it as well… It is a great relief to be rid of the book at last — sometimes I used to think it never would be finished, and that when I died I would order the single word 'Arc' to be placed on my tombstone as a pathetic record of my sufferings". She little knew what sufferings some of her future work would bring.

Her paper on "The Hissing Arc" was read before the Institution of Electrical Engineers, of which she was elected a Member, in 1899. Blondel, who, as I have said, had worked at the silent arc, and had been troubled with the hissing, esteemed her work. I was at the Cape at the time, and started the first Local Centre of the Institution of Electrical Engineers at Cape Town. At a meeting of the Centre, at the South African College, I read her paper, reproduced several of her experiments, showed a lantern-slide portrait of their author, and attempted to describe her charming personality.

One of the conditions of the steady burning of the arc is the shape assumed by the ends of the carbons. A large square-ended carbon takes twenty minutes or more to settle down quietly after hissing, or rather roaring. She found that by properly shaping the ends, the arc was in good order a few seconds after recarboning. Acting on this, the Admiralty and War Office standardized the carbons used for searchlights. Crompton had long before used small negative carbons in order to avoid the shadow cast by them. The limit of their size was their fragility, and sometimes they were run nearly red hot. Mrs. Ayrton suggested that they should be coppered to carry the current, and this was adopted both by the Admiralty and by the War Office. Soon after her death in 1923 I spoke about her work to a Royal Engineer Officer. He was contemptuously incredulous that a woman could have had anything to do with search lights. He had probably never seen any other kinds of carbons. On the other hand C. H. Wordingham, Electrical Engineer-in-Chief of the Admiralty, became well acquainted with Mrs. Ayrton's work.

It was rather unfortunate that she gave the title "The Hissing of the Electric Arc" to her paper. Those of her audience who had anything to do with arcs knew that they sometimes hissed and gave reduced light, but few of them attached much importance to it. For the London Press the important thing was that a woman should address an audience of engineers. She was described as "a little dark-haired, dark-eyed lady, wearing pince-nez, who created a sensation which perhaps accounted in some degree for the unusually large attendance of young men members"; and The Spectator observed with some superiority that it could understand the admiration excited by Mrs. Ayrton's lecture better than the surprise, and held that women have a distinct proclivity towards science and mathematics, finding them less exhausting than either history or mathematics".

These quotations from Evelyn Sharp's Memoir of Hertha Ayrton show the rubbish that we must expect from the Press when the ordinary journalist attempts to deal with science, while the Memoir is a striking instance of how a lay author, if the expression may be permitted, can write with accuracy and judgement on technical subjects.

She relates how Professor Ayrton had been requested by the Admiralty in 1903 to investigate the strange behaviour of electric arcs in powerful searchlights. "The four reports submitted to the Admiralty in 1904 - 8 were treated officially as his, although Mrs. Ayrton had assisted greatly in drawing up the three earlier reports, and the fourth was actually sent in over her own name because it embodied her unaided researches, and Professor Ayrton insisted that this should be made clear when it was forwarded to the Admiralty. The official mind, however, seemed unable to grasp that the work was not really done by the man who had been commissioned to do it; and perhaps it is unreasonable to expect too much of the official mind … the fee was sent to her husband".

Carbon manufacturers with whom Mrs. Ayrton was in frequent communication recognized the importance of her improvements. She was consulted by a cinematography company who wished to avoid the sputtering and hissing of small arcs. The behaviour of cored positive carbons in which a pith of soft material burns away and helps to hollow out the crater was well known to her, and she had used cored negatives. But a negative, having no light-emitting crater, should be pointed. Sometimes carbon is deposited on it from the positive, giving rise to irregular "mushrooming". She made experiments to improve the pointing of the negative, and, contrary to all practice, she made soft negatives with hard cores and patented the invention shortly before the War. The result was a practical success, but arc lamps are now being superseded, not only in cinemas but in street lighting by improved incandescent lamps.

The wrinkles and ridges of sand on the sea shore attracted her attention and scientific inquisitiveness. They bear some resemblance to the ripples on the surface of a liquid, but are obviously of a different nature. A long and intricate research was undertaken, and in publishing the results she decided to call them ripples. Vaughan Cornish had carefully studied, described and photographed waves of water, sand and snow, but that was not enough for Mrs. Ayrton. Like young Clerk Maxwell, she wanted to know "What's the go 'o that?". Cornish had made world wide observations. For Mrs. Ayrton a couple of square yards on the Margate shore sufficed.

I have only a copy of the first of her Royal Society papers to refer to, and a few of her letters to me, and will not go into details, but I cannot forget the beautiful experiments which I have watched. After her husband's death she turned the large drawing-room of her house at 41 Norfolk Square into a laboratory, and equipped it with glass tanks. Some were a yard long and about ten inches wide and deep, filled with water, and a layer of sand about an inch deep on the bottom. They were mounted on rollers and moved to and fro to make waves swing backwards and forwards. Some were kept in motion by electric motors.

The movements of waves and eddies of perfect fluids under assumed or imaginary conditions have been a favourite theme for mathematicians. It is necessary in such treatment to get rid of some of the practical circumstances. In the teaching of elementary mechanics inextensible cords run over frictionless pullies, in thermodynamics the behaviour of impossible engines is considered, and in electrical engineering, ironless transformers at one time occupied much attention. The results of mathematical investigations of waves and vortices have been expressed in mathematical terms. Mathematics is a method of description, and mathematical analysis is generally a reduction to a statement in the form of an equation. In many cases this result cannot be expressed in the language of words. Lord Rayleigh and Prof. George Darwin had made such calculations, but they had done more, for they were both experimenters.

Mrs. Ayrton began with pure experimental observation, and made few if any assumptions. It is difficult to compress her work into a few words. She began by making a ridge across the bottom of a tank, and set the water swinging to and fro. Water passing over the ridge curled down and formed a roller eddy or cylindrical vortex near the ridge, scooping the sand up backwards against the ridge. "After a few more oscillations not only did these grow into very decided ridges, but each of them had, in its turn, originated fresh furrows and ridges, and soon the whole of the space between the original ridge and both ends of the trough was covered with the ripple-mark".

The movement of the sand which at her will formed itself into beautifully regular patterns was apparent enough, and the wave form of the surface of the water was obvious, but between them existed the internal motion of the water. One of the ways in which she traced this was to put a morsel of permananate of potash on the edge of the ridge. The passing water swept a thin stream of coloured fluid and curled at first down, then backwards, and then upwards forming a complete spiral. In some experiments, in order to separate reciprocating movement from flow, she interposed exceedingly thin films of indiarubber. She eventually hit on the employment of finely powdered aluminum. This exhibited with perfect clearness the beautiful sight of a dance of silvery ribbons tracing out the eddies which she created. Needless to say, Lord Rayleigh fully appreciated the translation of his mathematics into this graceful form. He was that kind of man. George Darwin had made calculations in 1884 as well as experiments, and was not quite satisfied on some points, but welcomed her work. And there were other mathematicians.

In her research on the electric arc she had carried all before her, and produced the standard book on the subject; and she made herself mistress of sand ripples. As I have said, mathematicians had busied themselves with theoretical waves and vortices. I do not know if Mrs. Ayrton found that her practical observations conflicted with their rigorous results; probably not. When they were offered to the Royal Society, criticisms were raised, and she was sensitive about them, for there was an apparent conflict. Her paper was rejected by the referee; but Lord Rayleigh entered the lists, championed her cause, her paper was accepted, and the Hughes gold medal was awarded to her for this and her work on the electric arc. They accepted several other papers from her.

She met with a very different reception in Paris. Not content to demonstrate the formation of sand ripples, she investigated the movements of water, and contributed to the Société Francaise de Physique a paper on the formation of sand ripples and on the internal movements of water. To write the paper in French and fluently to deliver it in that language was no difficulty, nor was the transport of the glass tanks and other apparatus and the performance of the experiments a task beyond her powers, but a long paper on a very different subject was on the programme, and she was nearly crowded out. Such experiments as time permitted went off well, her interpretations were received and cordially appreciated, and the President said that in this race between experimental and theoretical science theory had for the present been overtaken, even existing mathematics were not able to deal with the subject, which remained to be explained by les mathématiques de l'avenir.

Her work on the electric arc aimed and arrived at practical results; her investigation of the production of sand ripples may be said to have been the outcome of scientific inquisitiveness; but she turned it to an application of great importance at that time, in the War. Those who saw her experiments at home or the results at the front cannot forget them, but few of the younger generation have heard of them, and that is why, admiring her work as I do, I will put my recollections on record. Early in 1915 the Germans with fiendish brutality began to use poison gas. She thought that eddies of air might be used to repel gas attacks.

Air is a very different fluid from water. The one has, in the scientific sense, low elasticity, its easy compression is accompanied by heating, it is light and almost impalpable; the other is almost incompressible, capable of massive motion and more obvious internal and skin friction. To anyone else the idea was so wild as to be absurd. But she was so thoroughly acquainted with her subject, and had such a sound knowledge of physics, that she saw that in dealing with fluids the question of scale was of little importance. To imitate a gas cloud she used the smoke of brown paper, but this while warm tended to rise above her laboratory battle field (the glass tanks and sand and water had been cleared away). Cooling chambers and pipes were devised and made, and smoke poured out and rolled along the floor. A few flaps with a card on a matchbox serving as the parapet of a trench drove it back.

I did not see the experiments until they had developed, and model "dug-outs" and "pill-boxes" had been built. These could be cleared of smoke with a few flaps of a tiny square paddle or fan. The fan with a flexible blade rather more than a square foot in size was mounted on a T-shaped handle. When smacked on the ground facing the on-coming gas, the cross bar of the handle hit the ground first, the blade flattened out, and sent a puff of air. The friction of the ground retarded the lower part of the puff, which became a vortex cylinder. When smoke rings are formed at the end of a gun, or the funnel of a locomotive, or the lips of a smoker, the central part of the puff advances faster than the edges, and so a ring is formed revolving on itself. Discussing this with Mrs. Ayrton, I asked where the ends of the vortex cylinder were, for I had the impression that a vortex ring must be continuous and cannot be cut. I cannot remember her reply, but it may have been that the under surface of the blade retards the air, and forms an upper vortex cylinder rotating in the opposite direction. But whether the two join to form a ring, I cannot say. An ordinary smoke ring increases in size as it travels, and induces a blast of air to pass through it. It was this that drove the gas back. Of Mrs. Ayrton's originality, perseverance and enthusiasm I was aware, but I found her greatly depressed, and showing a sensitiveness of disposition that was new to me. She could stand up to academical mathematicians, but now she was up against officialism. I must confess that the toy-like models in her laboratory-drawing room seemed a long way from the battlefield. So far as experiments went they were convincing when she showed them to me, and many who saw them, including intelligent soldiers, were impressed. But those who did not or would not come, and those who refused to give the invention a trial, the exasperating officials who would not listen to anything new because they shirked the responsibility of giving a decision, were obstacles with which she has not reckoned and did not know how to deal. The three years spent in brown paper smoke were not all concerned with research, that was soon done; her labour was to convince others.

I had nearly twenty years of government officialism, and already, during the war, something of the military variety. We discussed in confidence, without going into psychological analysis, the strange constitution of the official mind. I could only sympathize with her and show her that she was not the only special victim of obdurate nonchalance of those who were trained to be afraid of considering a thing on its merits, and so dutiful in clinging to a policy.

In spite of the disheartening opposition commonly shown to inventors at this time, several supplies of gas-repelling fans were sent to the front. These were not intended to be merely waved about, and perhaps the name "fan" was unfortunate. The inventor almost accidentally, perhaps intuitively, acquired the knack of using it in the best way, and this needed instruction. One of her assistants from the Central College went out and demonstrated the proper use of the fans, and a few officers were convinced of their value. If the reports which she showed me had been published, they must have come into general use, but the safest way to deal with a report is to consider it as confidential, and to put it away safely in a pigeon hole.

Discouraged and almost in despair after trying for two years to gain the attention of the War Office, she asked me to help her with the Admiralty. Thirty years had passed since I had dealings with that Service. I knew very few officers: Bacon had been a contributor to The Electrician, but he was at sea, and I recommended C. H. Wordingham, Electrical Engineer in-Chief of the Admiralty, with whom I was well acquainted. I have a letter from him dated Nov. 21, 1917, thanking me for the introduction and saying that he was going to see a demonstration. He was a practical engineer and was convinced on the spot, and thought that the use of such fans would be valuable for emergency ventilation of ships.

It must be remembered that when poison gas was first used in war, chlorine, a heavy gas, was blown across by the wind. The Ayrton fan was quite capable of rolling it back in the open, and, unexpectedly, even I think by Mrs. Ayrton, of clearing dugouts into which gas had fallen.

The practical successes of her sand ripple and of her fan experiments led to further researches in hydrodynamics. She read a paper before the Royal Society on "Local Difference of Pressure near an Obstacle in Oscillation in Water", using a manometer designed and made by her, and wrote another on the effect of skin friction on vortices. She discussed some of this work with me, and I could admire her skill in constructing the apparatus, and could follow the experimental work, but her mathematical discussion which always followed the observational part was beyond me.

To add to her troubles it was bitter for her to find that her active sympathy with the women's suffrage movement was impairing her scientific work and prejudicing her position. I think she never spoke to me of this until the last time that I saw her, when my wife and I visited her. Barbara Gould, her daughter, was present, and 1 learned what strong and extreme views they held on political questions. It was perhaps the only time, except once when I visited her and her husband during his last illness at Little Badow near Chelmsford, that we did not converse on scientific matters on which we could see eye to eye. She died in August 1923.

Hertha Ayrton was one of the last of the workers in physical science to start from experimental observation, to design and construct the apparatus in the laboratory, to carry through the research almost single handed, to discuss in mathematical language the process and the result, and to leave traces of the personality of the work in the method employed. Nearly all later work has been done with complicated commercial instruments in well-equipped laboratories, and is carried on by group or team-work, often under a director.