John thought the easiest thing to do after graduation was to stay on at Cambridge to do research and he applied for a DSIR-1- grant in the spring term of his final year. Before the end of the summer term, Professor Rutherford and a couple of the Cavendish staff interviewed the would-be research students one at a time, asking each what he would like to do as a project. John hadn't had any ideas at all so when it came to his turn he said that he would like to work on artificial radioactivity thinking that Rutherford would approve. In fact Rutherford was keeping his radioactivity projects for students who had achieved firsts."They all say that," he said with a laugh. "Now Dr Oliphant-2- has an experiment on gas discharges. You will enjoy that."
New research students were expected to come up for six weeks during the long vacation to acquire practical experience by working on a short project. They worked in an upstairs room called the 'nursery'. John had a partner called Waring, and the two of them completed their project to measure the efficiency of ionisation-3- of air by alpha particles over a range of pressures and applied voltages, with enough time to spare to extend the experiment by replacing the air with carbon dioxide, which turned out to be more efficient.
Building apparatus was part of every research student's work, and so a workshop course was run during the first term and John learnt useful techniques such as cutting nuts and bolts out of solid brass. A glassblowing course was also on offer, run by Felix Niedergesass the departmental glassblower, but there was a charge for this, which John did not feel he wanted to pay. However, a new Australian research student, Douglas Petrie, did pay for it and used to practise in the lab, so John copied all he did and by the end of the course felt himself to be a perfectly adequate glassblower, demonstrating his skills by making model animals from glass tubing.
There were other things to learn, not taught in any course. The chief technician, Lincoln, kept a very close eye on all supplies, giving out as little equipment as he possibly could and students became used to converting odd bits and pieces into usable apparatus. They also learnt a certain amount of psychology: if a student were to ask for half a dozen screws, Lincoln would accompany the supplicant to his bench, ask to see where the screws were to go, and issue the two that were actually required. If, however, a more wily student asked for seven screws, Lincoln would provide them without demur, assuming that such a request indicated a real need and a careful student. They found it was wise to screw any valuable piece of equipment such as a rheostat to the bench: if Lincoln found it loose, he was liable to re-issue it to someone else.
Cavendish, 1936, (3 megabyte picture)
The gas discharge project took the first year of John's time as a research student. A gas discharge is produced when electricity can be persuaded to jump through a gas at low pressure from one electrode-4- to another. This is the same effect as we see in the glow of a neon street light when an electric current flows through the neon gas present at low pressure inside the tube. The two electrodes are called an anode and a cathode respectively, and in gas discharges, under certain conditions, there is a dark space around the cathode. The aim of John's experiment was to compare the width of this dark space for discharges in hydrogen and in heavy hydrogen-5- respectively.
The apparatus required a large glass discharge tube fitted with electrodes to be made by Felix, a transformer followed by a rectifier to give 40,000 volts of direct current, an ammeter to measure electric current and a pump to create a vacuum inside the apparatus; everything had to be connected by wide diameter glass tubing.
The work proceeded with frustrating slowness. Felix did not produce the first tube until January, and from then on John did as much of his own glassblowing work as possible. The rest of the apparatus had to be leak-free, and achieving this was extremely difficult, for every bend or connection in the complex apparatus was liable to develop a tiny difficult-to-detect leak at any time. Many other physicists of the time were coming up against the same problem, and someone ruefully described physics as spending three days making your leaks so small it would take a week to find them.
Experience helped: one day Professor Rutherford walked round the lab to see how everyone was doing at a time when John was searching unsuccessfully for a very small but troublesome leak. Professor Rutherford surveyed the apparatus for half a minute and then put his finger on a bend that John hadn't suspected and asked if John had tried there. And there it was.
The electrical systems were somewhat primitive. The electricity supply to John's bench did not even come from a proper socket but consisted of two open terminals, controlled by a switch out of sight in another room. To save time he used to find out if the electricity was already switched on by putting two fingers of the same hand on the terminals very lightly and then increasing the pressure until he felt a mild tingle. His habit of wearing rubber-soled shoes made him feel quite safe. The only electrical measuring instrument John was given was a milliammeter-6- , suitable for measuring the gas discharge currents, but not for measuring the high voltages that had to be determined elsewhere. John added to the instrument a three inch by two inch wax block with six mercury-filled holes, two being permanently connected to the meter. Using brass hoops that could dip into the holes and various rectifiers and resistances a number of different arrangements could be used to increase its range, and to allow it to measure voltage as well as current.
Leaks were not the only problem: if something else could cause a bit of variety by going wrong, it did. By March, John had got the heavy hydrogen into his apparatus, but immediately his motor generator went wrong, and two days were lost while the assistants mended it. Then the wire supporting the reservoir for his pressure gauge broke and dropped the reservoir holding over six pounds of mercury. The wire caught in a clip before the glass actually broke, but some mercury was pushed into forbidden places, and John had to cut his way into his leak-free apparatus to clean it out.
By May he was getting some measurements of the cathode dark space, and he was able to extend the experiment to try the effects of different metals used as electrodes. He was a little disappointed that his results did not exactly fit any of the current theories of the cathode dark space, but he was sure he would be able to produce adequate explanations when the time came to write up the work.
While he was still in the Nursery, John joined the Cambridge Scientists' Anti-War Group, the effective head of which was Dr J D (Sage) Bernal, the crystallographer who first used X-rays to show the shape of a virus. The Group, which rapidly recruited a lot of young physicists and biochemists, was against the rearmament of both Germany and Mussolini's Italy. The members felt that Britain was unlikely to do anything about either country's activities while rearming herself and so the early efforts of the Group were spent in opposing British rearmament. John was prepared to do quite a lot as long as it didn't involve public speaking, and soon accepted the job of literature secretary, which meant buying six or more copies of relevant publications at a discount and selling them at full price. He built up quite a large paper profit, but always spent more on further books and pamphlets and finished up well in the red, covering the debts from his own pocket.
Caterpillars were still a hobby. When John arrived in Cambridge in August, he had some Occulta larvae with him. They were not growing very fast, and to discover the effects of keeping them warm, John divided them into two batches, and took one lot to bed with him at night. Unfortunately the results of this experiment have been lost to science. Surprisingly, he was always on remarkably good terms with his bedder!
Women were still difficult to approach. Every afternoon, all the research students and some of the Cavendish staff gathered in the library for tea. The small room was always crowded, and so tea was drunk standing up. One day, in January 1935, John noticed a pretty blonde girl he had not seen before, standing alone at the opposite side of the room. He had no idea who she was, but felt sorry for her and thought that someone ought to have introduced her to everyone, but was far too shy to go across the room and speak to her. By the next time he saw her, she had been allocated to a project with someone else. He was still attracted by his cousin Betty, but also managed to strike up an acquaintance with a girl called Mary, a biochemist, who also belonged to the Anti-War Group. She used to work late in Joseph Needham's lab most nights, but could sometimes be persuaded to break off for an hour to play squash.
But as time passed, John gained a little more social confidence. The Robertshaws ran a couple of holidays for young people, and John was happy to mix with the young women they selected for him to meet. He also met some of Celia's friends on occasional visits to Oxford. One particular friend, another Celia from Birmingham, attracted John's attention, joining the Fremlins for a holiday in Cornwall and for Christmas in 1935. John and the two Celias used to play a version of snap in which any pair turning up the same card had to quote poetry, changing from one poem to another as often as they liked, the first one to break down and stop being the loser. Both Celias were good at this, but John's sister did better, because she would improvise authentic-sounding inventions of her own if she ran out. She was usually caught out only because her voice would change in a characteristic way when she found herself getting away with it. John did not make any moves to get closer to his sister's friend, being unwilling to commit himself, although he did day-dream of eventually finding a job in Birmingham. His interest went unnoticed as he made little effort to charm, knowing of no way in which to do so and his conversations rarely touched upon personal subjects. He assumed that any friend, whether male or female, was as vitally interested in politics as he was at a time when, in common with so many other people at Cambridge, he was becoming very enthusiastic about communism.
Cycling was still John's preferred method of getting around, but the fact that Wallis had left Cambridge after taking his degree in geology to start work in Manchester reduced the cycling trips for a time, and they both regretted the lack of these outings. In February, Wallis suggested that they meet at some mutually accessible point for a cycling weekend. So John cycled to Leicester on the Saturday and met Wallis as planned at a cafe where they consumed tea number nine (a large one) before booking themselves into a cheap hotel where they spent the evening talking and eating Welsh rarebit. On Sunday they enjoyed a twenty-mile cycle ride through the Charnwood forest, separating at Loughborough in the early afternoon. John decided to take a train for part of the way, and cycled back to Leicester where he caught the train to Kettering. He spent the time on the train in writing a letter to his father, and then set off to cycle back to Cambridge.
John woke up in a strange bed next morning, with no memory whatever of how he had got there. He wasn't puzzled: he just thought: "Oh yes, Evelyn Nursing Home." Only after quite a time did he decide that there had to be a reason why he was there. Investigating himself carefully, he found he had a headache and a bruise on the temple and came to the conclusion that he had concussion and must have fallen downstairs in New Court.
In fact he had been found lying on the pavement beside his bicycle at Thrapston, six miles from Kettering, on an uphill stretch of road. The police had taken him back to Trinity, where he told Mr Dykes he was perfectly all right; Mr Dykes had doubted this and had had him taken to the Evelyn. There followed a great deal of speculation as to what had happened. John never ever remembered any of his journey home, and only achieved the vaguest memory of the time in Charnwood forest, but the letter he had written to his father was evidence that all these things had happened. The bicycle, which was found in low gear, was barely damaged, only the front wheel was slightly out of true. Nothing was wrong with his right side, which ruled out being hit by a car, and left only running into the kerb, a pedestrian or a dog. Mr Dykes and the nurses were puzzled by the fact that John was found with his pyjamas already on under his clothes, as if ready for a stay in hospital, but John knew that he would have put them on in the train in preparation for a cold winter ride.
Luckily, John soon found a new cycling companion closer to home when he befriended Douglas Petrie (from whom he had earlier picked up glassblowing) who had come to Cambridge from Australia. Douglas frequently turned up to share John's lunches, although it never seemed to occur to him to provide some of the food. They played tennis and squash together, and sometimes went out for cycle rides at weekends. John also joined the camera club, so that he could get the best out of the camera his father had given him for his twenty-first birthday. There he was given lessons on flash light work and developing his own plates, which were mostly pictures of caterpillars. He also learnt how to take pictures through a microscope, and to take infrared pictures.
The gas discharge experiments came to an end, and in his second year John was given a partner, Charles Smith and together they set out to make a neutron source, using deuterium (the brand new name for heavy hydrogen) and very high voltages. The basic idea was that if two atoms of deuterium, whose nuclei each consisted of one neutron and one proton, could be made to collide at high speed, two protons and one of the neutrons would 'stick' together to form a helium nucleus, and the remaining neutron would be free.
Many of the problems were similar to those of the previous year. In particular, a great deal of time was spent looking for leaks; the tubes connecting the parts of the apparatus had to have diameters of about two inches, which made creating bends difficult. Lincoln didn't believe in using expensive new brass tubing for such things and told John and Charles he couldn't find any when they asked for some, so they made do with odd pieces of cistern and water pipe. Plasticine was used to join the metal pieces of the apparatus together, which was very effective until the whole apparatus began to heat up when they first persuaded an electric current to flow through the contained gas and the plasticine started to melt. It did not cause any leaks, but grease from it ran through the cracks into various parts of the apparatus, which then had to be taken apart to clean it out. John found working with a partner to be a mixed blessing. Charles seemed to be very good at breaking things: with each breakage, John dreamt up a way of strengthening the apparatus so that that particular accident could not re-occur, and so quietly, without recriminations, took the necessary steps to protect the apparatus from his partner. It is of course quite possible that Charles also had reservations about working with John but also kept them politely concealed!
Slowly but surely they found ways of pushing the voltage up. By the summer they had achieved 54,000 volts and had produced their first neutrons. By the following Christmas they were working at 70,000 volts and producing large numbers of neutrons, but at this stage the apparatus struck back. John was using a glass handle to move part of the set-up when Charles suddenly saw a spectacular flash. John saw nothing but heard a loud crash, and found himself on the floor, with a paralysed hand still gripping the glass handle, which now had a piece of the apparatus attached to it, and with a distinct feeling that his arm had been cut off at the elbow by a blunt sword. This electric shock taught him to be more circumspect with the high voltages they were using, but also that they were not all that dangerous.
The rest of the third year was spent using neutrons for a number of experiments, one of which appeared to disprove some earlier Japanese work that reported the disintegration of neutrons -7- into protons and electrons. Subsequently just such a breakdown has been shown to occur, but John and Charles could not have observed the effect without having apparatus that was four or five times more sensitive than theirs was. However, at the time, they were confident enough of their results to send them in to "Nature" where they were published as a letter.
John was never as satisfied with the neutron work as he had been with the gas discharge experiments. It is true that he continued to learn a great deal about glassblowing, making apparatus and a variety of experimental techniques, but the subject was so new that the constant difficulties of breaking new ground allowed little time for meaningful experiments.
While John was still working on the neutron source, he decided to put in a thesis on his work so far in an attempt to win a particular Trinity award. He and his friend Bamford, who was doing some experiments involving ultraviolet light, worked together to get their theses written. Each weekday evening after dinner in Hall, they would go to Bamford's room in Great Court and, after he had done his music practice, they would get down to work. Someone had told them that when tired, people's temperatures went down, so John took along a clinical thermometer and measured their temperatures periodically. When their temperatures went down for the first time, they would stop work and have a cup of tea. The second time they would stop for a light meal and a chat and on the third occasion, usually after half past one in the morning, they would knock off and go to bed. John found that it took a long time to get to sleep after that, until he decided that it was due to the physiological effects of low body temperature. So each night after that, he used to go back to the baths in New Court and stand under a hot shower with the thermometer in his mouth until his temperature got back to normal, which took five to ten minutes. After that he would fall asleep as soon as he got to bed. Interestingly, it had never occurred to him to take such care of himself during his regular habit of reading until much the same time!
The thesis then had to be typed. John borrowed a typewriter from a zoologist friend who lent it on condition that John learn to touch type, which he did, but the typing was slow, and a great deal of eraser was used. At last a presentable thesis was submitted but sadly John did not win the award he wanted.
John's spare time was increasingly spent working with the Anti-War Group. Towards the end of his second year as a research student, the secretary of the Group left, and John took on the post. Soon Sage Bernal was asking if John would take over some of his anti-war speaking engagements, as he was finding it hard to find time to fit them all in to his notoriously busy life.
John had never spoken in public before, unless one counts one question he had asked with a hammering heart at a meeting when he knew the speaker had made a mistake. But he felt strongly about the issues involved, and agreed to help with some of the talks. He prepared himself for the first one by attending a lecture given by Sage in Cambridge and making detailed notes on what he said. He then wrote out his own version in full, adding two quotations to the start of the talk to give himself an excuse to start off by reading aloud. His first lecture was in the Forest of Dean, and was very kindly received although a lot of it consisted of descriptions of the molecular structure of mustard gas and phosgene. This could have meant little to a group of country members of the National Peace Council, and John felt that their very warm applause was due to pleasure at seeing a young scientist on their side. (Scientists then as now were often blamed as a class for making possible the horrors of modern war.) This gave him a modicum of confidence, and his talks steadily improved as he began to work out what his audiences might want to know. For a long time he suffered acutely from nerves, and found that the only way to prevent an attack of nervous diarrhoea immediately before he was due to speak was to miss a couple of meals before an engagement.
Another task the Anti-War Group set itself was to demonstrate the fact that the government was trying to lull the public into a false sense of security over the dangers civilians might have to face in a war. The government was not attempting to dispel the widely held belief that in the next war the Germans would use the gases deployed on the battlefields of the Great War against civilian populations but gas masks and instructions on gas-proofing rooms were being distributed widely in order to show that the situation was under control. The Anti-War Group were strongly of the opinion that these measures were unlikely to work so they equipped itself with all the advertised instructions and several gas masks in order to perform their own tests.
To test the instructions on gas-proofing rooms, some members of the Group followed them closely in preparing a room in Kings Parade. They then put a few pounds of solid carbon dioxide inside it, before closing the door leaving a tube poking through the keyhole held in place by plasticine. The tube could be connected via a tap to a succession of evacuated glass bottles that John had made. The idea was to take regular samples over the next 48 hours to be tested later for carbon-dioxide concentration, which would tell them if the room was sealed well enough to keep the carbon dioxide inside. None of the male members of the Group were allowed out of college after midnight, but Newnham post-graduates did not have to obey such rules. Reinet Maasdorp, the girl John had seen standing on her own in the Cavendish library was now an enthusiastic member of the Anti-War Group, and went out to the chosen room in the small hours to take a night sample. Her self sacrifice was wasted: after the first couple of hours, no further carbon dioxide could be detected in any of the collecting bottles they tested the next day; the gas had all leaked out despite the careful proofing. Several more experiments were conducted on different rooms, sometimes with John sealed inside to try and improve the sample taking. (He found that his heart rate increased at first because of the carbon dioxide concentration, but suffered no long-term effects.) The only place that could be successfully gas-proofed was the bathroom of a married member of the Group, which had a steel-framed window.
John did a further experiment of his own with tear gas. Waiting until the occupant of the adjacent set of rooms was safely away, he sealed his bedroom from both the gyp room and the sitting room, and released some tear gas on his bedroom chest using a string through the keyhole, which was blocked with plasticine immediately afterwards. He then visited the gyp room at intervals and tested for tear gas by assessing any effects on his eyes, and found that it definitely leaked through. However, even when he opened all the doors and windows, the tear gas took a long time to go, and was still at an intolerable level, even in the sitting room, when he wanted to go to bed. So he made up a bed in his sitting-room and put on a civilian-type gas mask. This was perfectly effective, but the rubber valve, which flapped at the end of every exhalation, kept him awake. At two o'clock, he decided that when he heard Trinity Clock strike the next half hour he would abandon the room and go up on the roof. This wasn't necessary: he then fell asleep and woke up drowsily soon after seven, still safely in the mask. But when he turned over he was woken properly with a jerk as several ounces of cold water, which had condensed from his breath, ran down his neck.
Soon after this awakening, his bedder and bedder's help arrived, in tears. They were extremely kind however: they not only accepted John's hopeful statement that the gas was only the result of a chemical experiment and should be gone by the next day, but also one of them went down to intercept the college porter who usually brought John's milk up the stairs.
Having shown that the official instructions for gas-proofing rooms were inadequate, the Group turned its attention to the instructions on how to deal with incendiary bombs. These said that an incendiary bomb should be picked up on a shovel and dropped into a bucket of sand or water. Incendiary bombs were made from thermite (a mixture of aluminium and iron oxide powders) in a case made of an aluminium and magnesium alloy. Both powder and casing could burn fiercely but needed high temperature ignition with flash powder.
John bought a few pounds of thermite and some quarter inch thick sheets of alloy from which he made hexagonal tubes to fill with thermite, and used some flash powder and a slow match to ignite them. The experiments were done over the Christmas holidays with Celia's help, starting on Christmas day 1936.
The first attempt to pick up a bomb on a shovel failed because the light was too dazzlingly bright to see properly. So John put on dark glasses and tried again. This time he could see the bomb well enough to get it on the shovel, but he couldn't see the pail of sand. So he decided to bypass the shovel by putting the next bomb on a thin piece of plywood over a bucket full of water. It burnt through the plywood at once, fell into the bucket of water, and burnt through the bottom of the bucket onto the ground below before going out.
The gas-filled room and incendiary bomb experiments were followed by tests on gas masks. The Group started by testing them with chorine and tear gas. Neither gas could be detected when air containing each of them was passed through the filters, and the filters showed a confirmatory increase in weight. But results with smokes were not so satisfactory. At the time, there were a couple of poisonous smokes available to a aggressor, diphenylcyanoarsine and diphenylchloroarsine, which, although not lethal at the levels at which they might be used, caused intense pain in the nose and lungs and induced vomiting at low concentrations, forcing a wearer to take off his mask and become vulnerable to other gases. Using a set-up that included a vacuum cleaner to blow a stream of air when required, cigarette smoke could quite clearly be smelt on the other side of a gas-mask filter. John demonstrated this effect at his public lectures by taking a good mouthful of cigarette smoke, donning a mask and blowing it through the filter for all the audience to see (notwithstanding his intense dislike of cigarettes). The first time he tried it, someone in the audience claimed that it was not a fair test because the mask was designed to stop smokes getting in, not out. So in later lectures, he started by taking the filter off the face piece while the audience was watching and turning it round so that he was blowing cigarette smoke through it in the right direction. The results were identical but more convincing.