20th c. Cowley automatic level

The Cowley level.
Figure 1: The Cowley level.
'In appearance this level does not look like an ordinary level but resembles a small amateur's cine camera. It is particularly suitable in building and engineering work for setting our [sic.] foundations, gradients, etc., and, although it can be used for running short lines of levels from point to point, it is not so suitable as an ordinary level for carrying forward long lines of levels. It has the advantage of being very simple and quick to use and it is very cheap considering the degree of accuracy obtainable with it. It has also the advantage of not requiring a skilled surveyor to manipulate it.'1

This is how the instrument is introduced to us in the fifth edition of Clark's Plane and Geodetic Surveying that spends three whole pages on the instrument.2

The Cowley level was invented by Australian Keith Cowley in 1944.3 As can be seen in figure 1 and figure 2 the above description was rather accurate. The instrument, tripod (see figure 5) and levelling staff (see figure 6) were all designed along very simple lines, reducing the number of parts in all these three components to a bare minimum. As above work credited Hilger & Watts for the drawings (see figure 16 and figure 17), it was most likely this firm that manufactured the instrument for Cowley.

The Cowley level from the other side.
Figure 2: The Cowley level from the other side.
The instrument is not even fixated to the tripod, but simply slides over a smooth pin to stay in place (see figure 12). On the rear of the instrument a warning was pasted not to carry the instrument around while mounted on the tripod for the evident risk of loosing it (see figure 2). The pin also releases the pendulum once the instrument was placed on the tripod.

The 'optics' are very simple as well. There are no lenses, just glass covered apertures, two mirrors at the left hand side of the instrument and tree mirrors at the right hand side (see L.H. and R.H. mirrors in diagram in figure 17 and picture in figure 18).

Although not the first automatic levelling instrument (for a discussion on that see the 1960s Zeiss Opton Ni 2 page), it possibly was the first popular one, although that was more thanks to its price than its performance. The Cowley level was invented roughly half a decade before the famous (and much more accurate) Zeiss Option Ni2.

Accuracy
Not much accuracy can be expected from a simple level like this, there are even no screws to adjust the instrument when needed. The manufacturer stated that it would be about "1/4 in. at 100 ft." (approximately 20mm/100m).4 The staff is metric, divided in half a centimetre intervals, and can be read by estimation at a millimetre level (see figure 9). As was more common in the late 19th and early 20th century it is not a self reading staff, but has to be read by the assistant if used for levelling. Most likely Cowley levels were however used as a modern rotating laser by setting the cursor at a certain level after which the levels of points around the instrument were verified.

The instrument
The instrument was donated to my collection in 2016, is in remarkable fine state and very complete. It came complete with its original leather case (with key!), tripod, a 1.5 metres wooden levelling staff, and a 2 foot cursor (see figure 7). Cowley levels are also known to have been sold with cursors of a foot and a half with a different pattern (see figure 8).

The staff and cursor are 'made in England'. Being divided in metres instead of feet, makes clear that the instrument was also produced for the continental market. This specific example was sold by Gadella, an Utrecht based Dutch firm known for selling Watts surveying instruments.5 They still sold Cowley levels in 1971, in which year a complete Cowley levelling set would have sold for fl.340,- (just over €610,- in 2013).6

The variable Fall or Rise 'slope' attachment

The variable Fall or Rise 'slope' attachment for the Cowley level.
Figure 3: The variable Fall or Rise 'slope' attachment for the Cowley level.
In June 2016 I was hinted that a variable Fall or Rise 'slope' attachment (see figure 3) for the Cowley level was available on an on-line auction. This simple attachment allows the Cowley level to be used to set out slopes with gradients up to about 1:10 (see figure 21). It came complete with its original case (see figure 20) and manual (see figure 24 and figure 25).

Internally the slope attachment consists of a pair of glass wedges that are mounted in plastic collars with toothed rims. A knob with a tooth wheel turns both collars simultaneously in opposite directions. This system was invented by Boskovic and Bosshardt and has also been implemented in tacheometers as the 1952 Wild RDH. When set at infinity the two wedges counteract each other exactly, while a rotation of both collars over 90 degrees results in a maximum slope double the value of each wedge.

The knob of the variable Fall or Rise 'slope' attachment is graduated from 10 to 50 and has a '0' mark (see figure 22). A blocking pin inside the knob prevents the knob to be turned more than approximately 340 degrees, leaving the zero mark at the side of the 50 mark. This zero mark was either for assembly or to indicate infinity (even though it is slightly off for that). The figures on the scale indicate the ratio of the slope, which is thus running from 1:10 (10cm per meter) to 1:50 (2cm per meter).

The whole attachment is mounted to the Cowley level using an elastic band. Four pins at the rear of the attachment prevents it from turning freely around the optical axis (see figure 23). It depends on the mounting direction whether the slope will be rising or falling (see figure 21 and figure 22).


Notes

[1]: D. Clark, J. Clendinning, Plane and Geodetic Surveying for Engineers, Vol. 1, Plane Surveying, (London, 1963), p.607.
[2]: Clark, Clendinning, Plane and Geodetic Surveying... Vol. 1..., (London, 1963), pp.607-609.
[3]: Commonwealth of Australia, Patent Specification 122776 (application date: 9th August, 1944), Great Britain patent GB19450027720 19451022 (Oct. 22, 1945).
[4]: Clark, Clendinning, Plane and Geodetic Surveying... Vol. 1..., (London, 1963), p.609.
[5]: Gadella, Prijscourant voor tekenaar en landmeter, (Utrecht, 1951), pp.91-98.
[6]: Gadella, Prijzenblad drieslagfolder: januari 1971, (Utrecht, 1971), p.2. Currency converted using International Instituut voor Sociale Geschiedenis: De Waarde van de gulden / euro.


If you have any questions and/or remarks please let me know.

The Cowley level came with its original leather case.
Figure 4: The Cowley level came with its original leather case.
 
The Cowley level also came with its original tripod and levelling rod.
Figure 5: The Cowley level also came with its original tripod and levelling rod.

The top section of the levelling rod. Both ends are protected by brass plates.
Figure 6: The top section of the levelling rod. Both ends are protected by brass plates.
 
The two foot Cowley cross that came with the instrument.
Figure 7: The two foot Cowley cross that came with the instrument.

Another Cowley cross from a befriended collector, this one is a foot and a half.
Figure 8: Another Cowley cross from a befriended collector, this one is a foot and a half.
 
The cursor is clamped to the staff using a dovetail construction and wingnut.
Figure 9: The cursor is clamped to the staff using a dovetail construction and wingnut.

The Cowley level was sold by the Dutch firm Gadella. The hole at the left is the ocular.
Figure 10: The Cowley level was sold by the Dutch firm Gadella. The hole at the left is the ocular.
 
The patents and serial number at the base of the instrument. The hole is for tripod mounting.
Figure 11: The patents and serial number at the base of the instrument. The hole is for tripod mounting.

The Cowley level is mounted on a single pin.
Figure 12: The Cowley level is mounted on a single pin.
 
The Cowley level as seen from the front.
Figure 13: The Cowley level as seen from the front.

A view through the Cowley level.
Figure 14: A view through the Cowley level.
 
The levelling staff and cross as seen through the Cowley level.
Figure 15: The levelling staff and cross as seen through the Cowley level.

An explanatory diagram of what you see (Clark, Clendinning, 1963).
Figure 16: An explanatory diagram of what you see (Clark, Clendinning, 1963).
 
The internals of the Cowley level  (Clark, Clendinning, 1963).
Figure 17: The internals of the Cowley level (Clark, Clendinning, 1963).

Another Cowley level opened to reveal its interior. R.H. 3 is the pendulum mirror.
Figure 18: Another Cowley level opened to reveal its interior. R.H. 3 is the pendulum mirror.
 
A close up of the small square pendulum mirror.
Figure 19: A close up of the small square pendulum mirror.

The variable Fall or Rise 'slope' attachment for the Cowley level with its original case.
Figure 20: The variable Fall or Rise 'slope' attachment for the Cowley level with its original case.
 
A close-up of the variable Fall or Rise 'slope' attachment in its 'rise' position.
Figure 21: A close-up of the variable Fall or Rise 'slope' attachment in its 'rise' position.

The variable Fall or Rise 'slope' attachment in its 'fall' position and the confusing 0-indication.
Figure 22: The variable Fall or Rise 'slope' attachment in its 'fall' position and the confusing 0-indication.
 
The rear of the variable Fall or Rise 'slope' attachment for the Cowley level.
Figure 23: The rear of the variable Fall or Rise 'slope' attachment for the Cowley level.

The manual of the variable Fall or Rise 'slope' attachment for the Cowley level.
Figure 24: The manual of the variable Fall or Rise 'slope' attachment for the Cowley level.
 
The rear of the manual of the variable Fall or Rise 'slope' attachment for the Cowley level.
Figure 25: The rear of the manual of the variable Fall or Rise 'slope' attachment for the Cowley level.

Surveyor's crosses Geodetic Sextants Theodolites Total Stations Levels Standards Tools Firms
20th c. hydrostatic level 19th c. water bottle level 19th c. Secrétan Egault 19th c. Tibaut Lenoir 1928 Carl Zeiss Nivellier I 1926 Wild NKII 1924 Carl Zeiss Nivellier II 1948 Wild N1 1932 Carl Zeiss Nivellier III 1951 Wild N2 1965 Wild NK01 1965 Wild NK10 1961 Wild N3 1970 Wild NK2 1977 Wild N3 1999 Wild NA2-GPM3 20th c. Cowley 1960s Jenoptik Koni 007 1960s Zeiss Opton Ni 2