‘We took the whole thing apart’ — conserving MOTAT’s Cambridge Meccano differential analyser
‘For a Meccano historian, this was fascinating to see,’ said William Irwin when he first looked at MOTAT’s Cambridge Meccano differential analyser.
William began work as a volunteer at MOTAT in mid-2001. He had long been a Meccano man and had a great interest in MOTAT’s Meccano differential analyser. He was able to date the differential analyser from the Meccano used to build it.
What is a differential analyser? It is a mechanical or electronic analogue computer used to solve complicated differential equations.
MOTAT had been given the Cambridge Meccano differential analyser in the mid-1970s. The machine was built at Cambridge University in the UK by J.B. Bratt and was used in the university’s Mathematics Laboratory until 1950. Professor Harry Whale bought the differential analyser for £100 and brought it to New Zealand where he used it at the Seagrove Radio Research Station, part of the University of Auckland’s Physics Department.
Once it was no longer needed at Seagrove, it was sold to the Department of Scientific and Industrial Research’s Applied Mathematics Laboratory where it was used until 1961. From the DSIR, the differential analyser went to the Wellington Polytechnic where it was used for teaching before being put into storage. In 1973 it was rediscovered by the Wellington Polytechnic principal, donated to MOTAT and shipped to Auckland.
When William Irwin joined the team, the differential analyser had not been on display at MOTAT for a number of years. The museum had commissioned a conservation report for it, and William agreed with the report’s recommendations for conservation rather than restoration, although he knew it would take a lot of work. In an interview recorded in 2015, he described the condition he found the differential analyser in after he got permission to begin work in late 2002 or early 2003.
‘There was a bit of rust on the axle rods which could be easily cleaned off. You get some emery paper, you rub it, and it’s nice and shiny again. The actual girders, which were painted, were a bit more problematic because where bits of the paint had flaked off, there might have been a bit of rust here and there. So how do you clean that rust off without the paint also being damaged?
‘And bear in mind, they didn’t want us to strip the whole girder and repaint it because this was not a restoration. … If it was a restoration, we would have stripped everything and repainted it, but this wasn’t allowed. … the reason being that there’s only one of these left in the world. It’s the only one, so you have to be careful with what you do. When we did finally get around to fixing it up, we were very careful to minimise the damage to the paintwork [and] just clean it up, so now, if you look at it, you’ll see that some of the girders look pretty scrappy with bits of paint missing. But it doesn’t matter. That’s how it is now and how we found it.’
William made some notes of what had to be done to conserve the differential analyser and ‘co-opted one of the other Meccano men called John Denton to assist me. … He was very practical.’
‘On the plotter side, some bits were extremely rusty, especially the angle girder runners. At that stage, I went to the [MOTAT Registrar] and said, “These are far too rusty, especially the plotter table. We can’t possibly use them, even if we clean the rust off. Look how bent they are. If we can get angle girders like that from the 1930s from elsewhere, can we replace them?” Yes, all right, but you must keep the old ones and label them accordingly. So between John and me, because we have a lot of old Meccano, we managed to source bits which looked equally old and used — you don’t want to put brand new stuff there — and from the 1930s. You can tell from the labels that are stamped on the part. If it was pre-war, it’s just stamped ‘Meccano’. If it’s post-war, which is also red and green Meccano, it’s stamped “Meccano. Made in England.” So we could source the authentic Meccano bits from that period and replace it.’
‘So what’s there today — not all the angle girders are original, but they are original from that period.’
William is a Meccano historian and knew that the colours of Meccano pieces had changed at various times. He was able to date the differential analyser from the Meccano used to build it.
‘This Meccano that it was built from was 1930s Meccano, and there were various colour variations during that period. Some of the bits were red and green. It was built just at the changeover of Meccano going from red and green to blue and gold. And it was very interesting to see the transition. There was one integrator — the last one — which was built in 1937 and that as mostly blue and gold. For a Meccano historian, this was fascinating to see.’
‘There were a lot of bent and twisted axle rods and girders as well, which we bent back as best we could. Axle rods, we straightened as well as we could. It came with a whole box of extra spare rods and girders and things, so if one axle rod was too badly bent, we replaced it with another axle rod which happened to be in the box. That’s the nature of Meccano — you can interchange bits and pieces.
William described how he and John Denton began the conservation of the differential analyser.
‘We took the whole thing apart … because [of] the gunk, you couldn’t do it any other way. You had to take the whole support structure apart and clean each bit and then put it back together. We took a lot of photographs … to make sure we could put it back together again in the same way.
‘Afterwards we coated the whole thing with special oil which would hopefully stop further rust because rust is very difficult. It can get into the metal and it can carry on rusting.’
‘We started off with two of the integrators. The two ones closest to the plotter. Originally, the differential analyser consisted of five integrators plus a plotting table. Two plotting tables but one plotting table had got lost. … The two integrators and the plotting table had been operational in the ’70s [at MOTAT] until the ’80s. It was only demonstrated on occasion, but it was operational. So those were the two integrators we started work on.
‘The integrators are discs with a lot of Meccano … things coming off them and they are connected together with axle rods and gears and what have you. These are called wheel and disc integrators.’
Once the first two integrators had been conserved, William and John had to decide what to do next. They thought about the other two integrators. ‘John looked at the plotting table and said, “We could do that.”’ William was doubtful, as the plotting table was made from fibre board with metal sheets on either side. ‘Some of these sheets had got lifted up and bent. It was horrible. He said, “No, no. We can get it going. All we need is a few clamps and this and that.” I said, “All right.”
‘He brought the clamps the next day. … With his expertise, we got the plotting table restored to an acceptable appearance’ in 2005. The other two integrators were next in line.
After being conserved, William and fellow volunteer Gary Higgins decided to get the analyser operational, which they succeeded in doing in 2008. The operational differential analyser was part of MOTAT’s exhibition, ‘I Am the Last Tram’ dealing with life in the 1950s, which opened in 2011. In the meantime, William and Gary cleaned up the fifth remaining integrator. The complete analyser, with all fiveintegrators, is currently on display in the ‘Get Smart’ exhibition at MOTAT where it can sometimes be seen working — solving the differential equations that it was designed and built for 80 years ago.
Cite this article: Hutching, Megan. ‘We took the whole thing apart’: Conserving MOTAT’s Cambridge Meccano differential analyser. First published: 6 October 2020. URL: https://medium.com/motat/we-took-the-whole-thing-apart-conserving-motat-s-cambridge-meccano-differential-analyser-3119e035711
References:
J B Bratt et al. Circa 1936. Differential Analyser [Meccano], 2008.18. The Museum of Transport and Technology (MOTAT). https://collection.motat.org.nz/objects/47995
William Irwin et al. 08 Sep 2015; 22 Sep 2015. MOTAT oral history interview with William Irwin, 16–0540. Walsh Memorial Library, The Museum of Transport and Technology (MOTAT). https://collection.motat.org.nz/objects/92718
J. Crank. 1947. The differential analyser, PUB-2019–8. Walsh Memorial Library, The Museum of Transport and Technology (MOTAT). https://collection.motat.org.nz/objects/110260
