## John Denison Remembered

*by David Davies & Ron Lewin*

In the late 1970s my computing department at Fulmer was increasingly being asked for services which required serious mathematical modelling beyond our existing maths expertise. We also saw opportunities for uncertainty analysis which would require us to strengthen our theoretical understanding. At that time the only investigator at Stoke Poges with a maths degree was Rex Waghorne, who was fully occupied with projects in the physics department, so in 1979 we decided to recruit.

My preferred candidate was a remarkable man called John Denison. He had one big disadvantage – he was 59 years old. I had to argue long and hard for approval of his appointment. Colleagues said that by the time he had learned Fulmer’s ways it would be time for him to retire. In fact, John had a young family and he was hoping to work beyond retirement age, which is how it turned out.

John was intellectually brilliant. He had obtained a first in the Mathematics Tripos at Cambridge in two years, completing his degree by also obtaining a first in Mechanical Sciences.

John spent most of his career with English Electric at Stafford. In his early days there he wrote software for very early computers. He was seconded to the National Physical Laboratory, where he learnt to program the ACE Pilot Model computer designed by Alan Turing. Returning to English Electric, he worked on a fully engineered version of Pilot ACE, the DEUCE (Digital Electronic Universal Computing Engine)*.*

*An installation of the DEUCE computer ^{1}*

He wrote the first compiler for the early high-level language Alphacode^{2} and was described by John Boothroyd, a senior DEUCE programmer as “The brightest engineer and programmer in the team.”^{3} His light-hearted side was also to the fore; David Leigh, another EE colleague recalled that “John (known as “Speedy”) was responsible for the music programme. We used to gather round the DEUCE at Christmas time to listen to it playing carols.”

John was an early proponent of using computers to solve engineering problems. His mechanical engineering investigations at EE included the calculation of the critical speeds of rotating machinery, the natural frequencies of turbine blades and the use of statistical methods to predict the strength of brittle materials. An example of his work in electrical engineering was the calculation of the instantaneous voltages and currents in multi-phase rectifier circuits. He specialised in finite-element analysis, and was one of the authors of BERSAFE, the software package developed by the CEGB.

When John joined us at Fulmer in 1979 it soon became clear that along with his very profound knowledge of maths and computing John was a very practical man. Faced with an engineering problem, his first resort was sometimes to his beloved No 10 Meccano set.

We were able to use his expertise in finite-element analysis in projects ranging from the design of aluminium window frames to minimise heat transmission to the prediction of rock-bursts in deep hard-rock mining. Other examples of his Fulmer work included the design in composites of an aircraft component with a very exacting mechanical specification, prediction of the composition of copolymers and the solidification conditions in continuously-cast metal.

As a person, he was polite and friendly to all and had a rather self-effacing manner but he was a strong character. He had very firm ethical commitments; he declined to work in support of military projects and, in our cost-benefit analyses, he was unready to assign a value to a human life – even an infinite value!

He taught me a lot and I count it a privilege to have been a friend and colleague.

*1 Picture copied from http://www.members.optusnet.com.au/deucepix/pjwalker.htm*

*2 http://users.tpg.com.au/eedeuce/people.html#34*

*3 **http://www.members.optusnet.com.au/deucedocs/jboothroyd.html*

**2 John Denison – a beautiful mind**

by Ron Lewin

As well as his mathematical modelling work John made a considerable input to Fulmer’s project linking schools with industry. John also helped me with a series of talks at the Royal Institution on subjects containing a mathematical element. At such times I would give him my lecture to correct any mathematical errors beforehand.

On the occasion of the Earth Eclipse in 1999 John designed a machine to attach to one of our telescopes. His practical skills were of a high standard. Given a small lathe and a large box of Meccano he was in his element.

*One of John’s sketches – Heath Robinson meets Leonardo da Vinci.*

On the subject of working with schools one project was to show how useful computers were, which at the time were rather primitive. John chose to illustrate this with a competitive game that is very motivating – called the ‘rat in the pipe’. The idea was to drop a rat down the inside of piece of plastic down pipe and hit the rodent with a stick when it came out of the end. John wrote a computer program to do this. First the students armed with a stick were to hit the rat as it left the end of the pipe: this turned out to be a very difficult task but John substituted a student with a computer and lo and behold the exit of the rat was recorded precisely every time. This was very successful and the students saw at first-hand how clever modern computers could be. For the more squeamish reader I need to mention that a knitted rat was used.

The name of the Royal Institution demonstration lecture was ‘What is the Time?’. One of the high points of the lecture was to suspend a pendulum from the top of the dome and demonstrate the classical equation. I had always understood that the time for the complete precession of a pendulum was 24 hours but in the first few pages of Umberto Eco’s book ‘Foucault’s Pendulum’ which takes place at the Cathedral in Paris, states that the pendulum took 32 hrs. I mentioned this apparent elementary error to John who thought for a little while and then exclaimed ’Sorry – but I believe Umberto Eco is quite correct’. Typical of John, he subsequently sent me a handwritten manuscript on the relationship between the time of one precessional rotation and the latitude of the pendulum. The analysis showed that one complete rotation of a pendulum is 24 hrs – but only at the Poles. His explanation was later backed by a set of beautiful computer precession plots of a pendulum at different latitudes.

*Foucault’s Pendulum
*

*John’s plots of the precession of the plane of oscillation: Left high latitude and Right low latitude*

His apologetic, understated style was appreciated by many staff at Fulmer who benefited from the gentle help of a professional mathematician.

On behalf of his many friends at Fulmer – Thank you John.

FRHG ref: V850

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