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ON THE BUBBLE

Andy Foster, Raise Architects

In the corner of the studio, a wooden tripod leans against the wall. On the floor beneath it is a rectangular leather case with a damaged shoulder strap. The case houses a levelling instrument that, when assembled atop the tripod, provides the means of carrying out a level survey of a site or parcel of land.

Although it couldn’t be described as an antique, dating only from the 1950s or ‘60s, its form of manufacture would be recognisable to any land surveyor from around the mid-Victorian period onwards. The tripod comprises circular section bentwood legs each with a metal tip and step plate for pushing into the ground. The three legs are connected with a cast metal assembly that allows the legs to hinge and provides the support to a threaded ring that receives the level. Towards the bottom of the legs is a leather strap and buckle that holds the legs together when not in use. The instrument itself is mostly made of brass with a deep green enamel finish. It is essentially a rotating telescope that needs to be set precisely to the horizontal. To this end, its base attachment includes a spherical surface around which is a large serrated nut – this allows the device to be positioned approximately level by eye. Fine-tuning can then be carried out by reference to an integrated circular spirit level or bubble level.

The level has various devices for adjustment. A flat silver turntable enables it to spin around on a horizontal plane so that it can be pointed towards features of interest and a small metal lever acts as a brake to lock it in position. The telescope installation has a hinge at its centre so that it can be further adjusted for level by means of a knurled knob which moves it up or down at one end while being resisted by a spring-loaded spigot at the other. Each time a reading is about to be taken, this latter arrangement is used to adjust for the horizontal using a linear spirit level alongside the barrel and which has a hinged mirror to aid viewing. The eyepiece of the telescope rotates in order to focus on the internal cross-hairs. Finally, there is a second knurled knob to the side that adjusts the positions of the internal lenses in order to focus on a measuring staff.

The centreline of the level, when rotated, describes a horizontal plane. This means that, with somebody holding the measuring staff on features of interest, the vertical dimension can be read from that position up to the horizontal plane. It is most commonly used to measure features on the ground which are below the horizontal plane but it can also be used to measure higher-level features that are above the horizontal plane. To provide consistency of measurement, a permanent feature is usually chosen to which all other measurements are made relative. The level of this feature is known as the datum.

The instrument that I have just described is known as a ‘dumpy level’, so-called because it is a compact version of whatever larger and more complex contraption that preceded it. The dumpy level that resides in the corner of my studio was my father’s and I have known about its workings since I was approximately 10 years old when I became ‘the other

person’ that held the measuring staff. But I don’t keep it to hand for reasons of family nostalgia – it’s more because it provides a form of connection to all of the surveyors and engineers of the 18th and 19th centuries who mapped the world and its high mountains, the Ordnance Survey in the UK and the routes of our canals and railways.

These days when we need a level survey we ring someone up and they carry it out digitally. The digital instrument they use locks on to the modern Ordnance Survey GPS grid and for every position of interest that is measured, they obtain the 3D coordinates and not just the levels. It’s potentially easy, accurate and more reliable. But, as with most technological developments, something is lost in the process. In this case, there is a division of labour that can lead to a loss of understanding – either about the terrain being measured or about the process itself. Modern digital devices also contain complex electronics which are impossible to repair yourself when things go wrong. And don’t get me started on the subject of batteries.

When young architects join our practice they are invited to learn how to use this dumpy level and then they carry out level surveys for themselves. This usually causes much merriment in the office as the ‘old boy’ explains the workings of his old-fashioned equipment. But once the giggling has subsided, it is interesting to see the more experienced architects taking pride in instructing the novices. They seem to appreciate that doing things manually leads to a better understanding. They also sense that this is likely to apply to all digital developments and that being able to move easily between digital and analogue techniques is a real benefit. I imagine them thinking this while they’re listening to their vinyl record collection.

Image: Raise Architects