University of Cambridge

125 Years of Engineering Excellence


The Lab Pre-War

Dr Alan PercivalDr Alan Percival was a Fellow of Jesus College from 1938 (the first ever Engineering fellow of that college) and a lecturer in Engineering from 1946 - 1978. He worked as an assistant to Professor Inglis, and later was in charge of the Mechanics Group. We are grateful to his widow Mrs Moira Percival for supplying these notes, written by Alan, about his time in the Department, pre-war.

I came up to read Mechanical Sciences in 1932, and was of course delighted to cross the threshold of the Engineering Lab. It was the place where I could forget the horrors of school chemistry and learn to apply the physics and mathematics that had interested me.

I was of course familiar with steam locomotion -even steam road vehicles -but intrigued to learn the extent to which steam power ruled industry. The Heat lab was full of stationary engines, mostly presented by their manufacturers. If I remember correctly, one had a high- pressure turbine stage, and another high, medium and low pressure cylinders. True, there was one internal combustion engine -a single-cylinder gas engine with "hit-or-miss" governor. The steam engines needed a boiler-room to feed them and a condenser pit. As far as I know this took cooling water from the mains, not the Cam. The workshops were powered through a system of overhead shafting with belt-driven machine tools. We learnt how to assess efficiencies using Steam Tables and Charts showing Total Heat (later called enthalpy), Internal Energy, and entropy as functions of temperature and pressure. The intricacies of valve gear as displayed by "valve diagrams" told us when to expect a steam valve to open or shut, and why a steam locomotive could go just as well and as fast backwards as forwards, effectively by shifting the position of the eccentric driving the valve gear. Performance was assessed by mechanical "indicator diagrams" of cylinder pressure against position in stroke, and by engine speed and brake torque -measured by brakes of course.

The Structures lab was full of testing machines with loading ranges from one to five hundred tons. Among the staggering things one learnt was that steel had a yield point -and that the metal after yielding could be returned to its original condition by boiling. We enjoyed the messiness of mixing concrete test pieces of varying sloppiness and learnt that "in the field" it was difficult to get any testing done other than the "slump test" in which a bucket was filled with freshly-mixed concrete, turned upside down like a sand castle, and the mix okayed if it did not slump too far.

I was less familiar with the Electrical side of things. There was less to learn -no transistors, and triodes and pentodes working from lead-acid batteries to power even advanced "wirelesses" with loud speakers. That side of electricity was not engineering. I remember (as a boy) taxing my father for calling the outfit he was assembling a "wireless set" when it .seemed to contain miles of wires which he wound into coils. It did also contain a crystal and a cats-whisker to tickle it with, and "London calling" could eventually be heard on ear- phones. No, Electrical Engineering meant D.C. motors. The lab had a battery of enormous storage cells which I understood were mysteriously kept topped up from the mains through an imposing glass bulb some three feet in diameter -I think I was told it was a mercury-arc rectifier. Testing of electrical machines of course meant recording amps, volts, speed and brake torque -with a brake. Generally speaking, that is; but there was an outstanding exception -a "back to back" test in which two machines operated on a common shaft, one as motor driving the other as a generator which supplied the motor. The external source thus only had to supply the "losses".

In the Inglis building the structure and heat labs were much as they are now. The electricity lab was smaller and had no gallery .The large drawing office extended over LT1 and LT2. A Victorian residence, Scroope House, provided office accommodation which sufficed until the Baker building was erected -the first post-war building. There were also first-world-war army huts, quite capacious, to complete the picture.

One advantage of being a bright undergraduate in those days was that the Cunard Line offered free return trips across the Atlantic. If chosen, one travelled as a sort of engineer officer trainee, spending some hours daily watching what went on in the engine room, and for the rest eating with the Officers (First Class menu) and consorting with the Second Class passengers (bevies of attractive young American girls). I kept a fourth year as a research student. Although the higher degrees (Sc.D., LI.D. D.D. etc) were highly prized in those days, the Ph.D. counted for very little. It was not in the least necessary for an academic appointment, so I was not expected to start on a project and stick to it, but rather to be around the place and absorb its atmosphere. Thus I was engaged as "dogsbody" by R. D. Davies who was investigating rail joints for L. M. S. Our work involved having a typical stretch of line and a locomotive and wagons at our disposal, so that we could record rail profiles at joints and compare the motion of an axle as its wheels passed over the joint. A purely mechanical device had to be invented for this aspect of the project. On another occasion I was assistant to Professor Inglis. As an authority on vibrations he had been consulted by the management of a hospital (formerly an asylum) in Surrey. This stood at the top of a considerable hill, and its water supply was extracted from a well over 100ft deep. The pump was necessarily at the bottom of the well. I suspect that the original system was driven by a donkey going round and round, but it had been replaced by a rotary pump driven by a motor via a shaft which was concentric with the pipe up which the water was to flow, and from which it was supported by bearings at intervals of 12 feet or so. Not unnaturally, when the system was started up the pipe and shaft distorted into a snake-like form and the whole outfit whirled violently, the pump itself flying round most violently of all. Not surprising that an expert was call in! My job was to be lowered down the shaft sitting on (and roped to) a board. There I operated a lab-designed vibrometer to record the contortions of the system at various points in its length and at various speeds of rotation. It was a scary job, but fortunately the good Professor thought he'd got all the information he needed before I was more than half-way down. I was never informed how the Professor advised them, but that sort of experience certainly helped me to absorb the "atmosphere", and perhaps helped Inglis to assess me as a possible future colleague.

I say that logically, because at the end of my undergraduate years, the Senior Tutor of Jesus had advised me not to take up an appointment I had been offered, as the College wanted to appoint its first-ever engineering Fellow instead of using an "outsider" as director of studies and supervisor; and (if I liked the idea) I might do. What he told Inglis, if anything, I shall never know, but certainly Inglis had a closer look than exam results alone could give him. How sensibly things were arranged in those days -no compulsory advertising, no discrimination, just know your mind and act accordingly. Thus with recommendations from my College and the Department I spent two happy years as a graduate student in the U.S.A., one at M.I.T. and one at Harvard, generously funded by the Harkness Foundation. Returning in June 1938 I was forthwith admitted as a Research Fellow by Jesus (my first pay day was not until after the Audit of the 1938-9 accounts, i.e. in December 1939). I was also assured that a University Demonstratorship was waiting for me -nothing in writing, I was just to report at Scroope House on lst October, when I would be informed what duties would be assigned to me. How delightfully casual by today's standards, when nobody trusts anybody to take responsibility for anything without the support of a committee! My first lectures were on hydrostatics and given to an ordinary degree class. I found the teaching labs little changed and could be assigned demonstrating in the structures or heat labs. Internal combustion engines were beginning to arrive in the heat lab and remarkably we had been presented with an eight-cylinder aero engine with a cut-away cylinder block so that the "works" could be seen though not moved.

A monster which I well remember was a single-cylinder "hot bulb" engine. This had a dome on the cylinder head which had to be heated by an external flame before the engine would start. Once started, the internal firing kept the bulb hot enough so that the fuel ignited somewhere near the end of the compression stroke.

The Lab was primarily a teaching institution, and research facilities were minimal. I followed the established practice and got a Long Vacation job with de Havilland's, being attached to a team working on the vibration problems of Spitfires and Hurricanes, their engines and airscrews. The team was led by an ex-Cambridge engineer. Cambridge engineers were taught engineering, not confined to a single sub-branch, and the Engineering School had a nation-wide reputation unrivalled by other universities.

Dr Alan Percival
Fellow of Jesus College, 1938
Demonstrator in Engineering, 1938 - 1946
Lecturer in Engineering, 1946 - 1978