Details

The monument includes an extensively intact 19th century horse engine adjacent
to the northern farm building of Lower Town Farm, St Agnes, the south western
inhabited island in the Isles of Scilly. The monument also includes the horse
engine's drive shaft, passing beneath the farm building's wall, and the
threshing machine that it operated, situated against the inner side of that
wall.
The horse engine survives with a raised sub-circular earthen platform abutting
the northern wall of the barn in a complex of farm buildings. The platform
measures 9.75m east-west by 8.75m north-south across its base, and rises 1m
high from the adjacent farmyard. A narrow access ramp extends 3.5m south from
the south west corner of the platform, merging with higher ground around the
north west corner of the barn. The platform's steep sides are revetted by a
drystone rubble wall, while a thick turf over its upper surface masks evidence
for the usual paved hard-standing along the peripheral route trodden by the
horses.
The platform supports iron fittings for a `sweep' type horse engine, a form
where the drive shaft to the machinery extends from the base of the
horse-engine's central axle. The surviving fittings include a vertical axle,
1.2m high, ribbed along four edges and tapered to the upper end; at its lower
end is a 54-toothed gear wheel. Immediately above the gear wheel, the axle
passes through a slender framework forming a short girder which projects south
on the line of the drive shaft and retains a small 9-toothed cog against the
gear; the girder has a pivot by the axle, enabling the cog to be raised clear
of the gear wheel to disengage the drive shaft. Beyond the end of the girder,
at least one flat square stone slab survives over the drive shaft's bedding
trench which extends south across the platform surface to the lower wall of
the adjacent barn.
Two driving arms radiate from the axle, 90 degrees apart and linked by a
cross-bar, for two horses to power the engine, but of a design giving the
potential for a four-horse drive. Each driving arm consists of slender upper
and lower spars, converging on the arm's terminal from the upper and lower
ends of the axle. The tip of one arm still retains the long U-shaped bar,
called a trace, to which the horse was tethered; the trace enclosed the rear
of the horse and survives complete with hooks near the open end for securement
to the harness.
The drive shaft remains in place, passing through the lower wall of the barn
and ending at a large cogged drive wheel, c.1.2m in diameter and parallel with
the wall's inner face, its lower edge running in a pit below the barn's floor
level. This drive wheel engages with the drive gear wheel of a small
timber-framed threshing machine standing on the barn floor. The threshing
machine, c.1.7m long and 1.14m high, takes the form of an enclosed wooden body
raised on four legs; on the top is a feed surface and hopper leading to the
wooden casing of the threshing cylinder. The machine's drive wheels are
mounted on the ends of the cylinder axle which projects through the casing at
each side; the drive on the north end is the gear wheel engaging with the
drive wheel on the horse engine drive shaft; on the south end is a belt-drive
wheel enabling the machine to be operated by an auxiliary power source.
In the north wall of the barn, east of the threshing machine, a small window
opens onto the horse engine platform allowing the operation of the engine and
the threshing machine to be coordinated. Another feature relating to the
barn's former use, not included in this monument, is an opening in its east
wall allowing the grain crop and the threshed straw to be transferred from and
to storage in the loft of the adjacent building, whose stalls and surface
drains denote a former cattle shed, called a shippon.
The roof and guttering of the barn are excluded from the scheduling but a
section of the wall, floor, wheel pit, all parts of the horse engine and
threshing machine and the ground beneath them are included.

MAP EXTRACT
The site of the monument is shown on the attached map extract.
It includes a 2 metre boundary around the archaeological features,
considered to be essential for the monument's support and preservation.

Source: Historic England

Reasons for Scheduling

The Isles of Scilly, the westernmost of the granite masses of south west
England, contain a remarkable abundance and variety of archaeological remains
from over 4000 years of human activity. The remote physical setting of the
islands, over 40km beyond the mainland in the approaches to the English
Channel, has lent a distinctive character to those remains, producing many
unusual features important for our broader understanding of the social
development of early communities.
Throughout the human occupation there has been a gradual submergence of the
islands' land area, providing a stimulus to change in the environment and its
exploitation. This process has produced evidence for responses to such change
against an independent time-scale, promoting integrated studies of
archaeological, environmental and linguistic aspects of the islands'
settlement.
The islands' archaeological remains demonstrate clearly the gradually
expanding size and range of contacts of their communities. By the post-
medieval period (from AD 1540), the islands occupied a nationally strategic
location, resulting in an important concentration of defensive works
reflecting the development of fortification methods and technology from the
mid 16th to the 20th centuries. An important and unusual range of post-
medieval monuments also reflects the islands' position as a formidable hazard
for the nation's shipping in the western approaches.
The exceptional preservation of the archaeological remains on the islands has
long been recognised, producing an unusually full and detailed body of
documentation, including several recent surveys.

The animal-driven mill, usually using horses or donkeys walking a circular
track and harnessed to an arm which turned a rotating structure, has been
known since the Classical Roman period but received only limited application
until the early post-medieval period (from AD 1540) when it came into more
widespread use as the horse engine, often called a `horse whim', for powering
ore hoists and water pumps in the mining industries.
The horse engine only appeared in farming contexts in the late 18th century
technological revolution which gave a rapid rise in agricultural output and
which both reflected and caused a shift of labour from the land. It was the
invention of threshing machines to replace hand-flailing from the 1770s that
made the horse engine a necessary part of many farmyards.
The early agricultural horse engines tethered the horses to forks hanging from
poles radiating above the animals from a central wooden vertical axle
pivotting on iron pins; the poles turned a large wooden crown gear at the top
of the axle and the crown gear turned a small pinion on the end of a drive
shaft which took the power into the threshing barn. The horse engine was
usually situated outside the long wall of the barn and often enclosed within a
round or polygonal building, with the top of the axle pivotted into a roof
beam. The overhead gearing required an elaborate superstructure which also
limited the size of the horses' track and the power of the engine. These
problems were overcome with the invention of the `sweep' type of horse engine
in 1841, in which cast-iron gearing at the base of a short central axle turned
a drive shaft at or sunken below ground level. The horses were tethered in
traces fastened to metal arms radiating from the axle and their track passed
over the drive shaft on an iron bridge if the shaft was at ground level. The
sweep horse engines were usually in the open air, with a levelled track either
raised on a platform or slightly sunken into the farmyard. Threshing machines
also underwent development, incorporating winnowing mechanisms, improving
their efficiency and reducing damage to straw needed for thatching, and
becoming available in a variety of sizes, wheeled or stationery, with
differing capabilities for depositing or bagging the straw, grain and chaff
produced. By the late 19th century, the horse engine had been superseded by
the development of the portable steam engine, which, with portable threshing
machines, could be transferred from farm to farm and operated out in the
fields.
This monument at Lower Town Farm contains an unusually intact survival of a
sweep type of horse engine. Although horse engine platforms are known at a
number of farms, such extensively complete presence of the associated metal
fittings and gearing is very rare and is further complemented in this instance
by the survival in situ of the drive shaft passing through the barn wall,
complete with its drive wheel in the barn's wheel pit and engaged with the
threshing machine that it operated. As a result, this monument demonstrates
well the full set of operating components from a major, if short lived, phase
in the development of agricultural power sources, which had far-reaching
social consequences in the rural economy.

Source: Historic England

Sources

Books and journals
Brunskill, R W, Illustrated Handbook of Vernacular Architecture, (1978)
Brunskill, R W, Traditional Farm Buildings of Britain, (1987)
Other
Parkes, C/CAU, AM 107 for Scilly SMR entry PRN 7655, (1988)
Ratcliffe, J & Parkes, C/CAU, Fieldwork in Scilly: September 1989, (1990)
Title: 1:2500 Ordnance Survey Map; SV 8708
Source Date: 1980
Author:
Publisher:
Surveyor:

Told during MPPA visit 1/7/1993, Information spoken to MPPA by Mr Francis Hicks, Lower Town Farm, (1993)

Source: Historic England