16.
germ of government sponsored mapping.
Thereafter Roy was commissioned and before
he was 40 a Royal Warrant appointed him
"Surveyor General of Coasts and Engineer for
making and directing Military Surveys in
Britain". He became well known in the scien-
tific circles of the later 18th century.
Elected a Fellow of the Royal Society, he
read papers on "Rules for Measuring Heights
with a Barometer" and "An Account of the
Trigonometrical Operations by which the
Distance between the Meridians of the Royal
Observatories of Greenwich and Paris has
been Determined". Years before he became
Major General, he had continually advocated
a national survey of all Britain, to be the
basis of a series of maps at One Inch to the
Mile.
The Transactions of the Royal Society
also included his "Account of the Measure-
ment of a Base on Hounslow Heath". It was
accomplished between April and August 1784
over about five miles. Preliminary measure-
ment was by a steel chain ordered from the
eminent instrument maker Jesse Ramsden. The
exact length was measured by long one-inch
diameter glass tubes, and recorded as 27,404.01
marked by wooden pipes at each end. These
tubes, up to 26 feet long, were the spon-
taneous idea of a young officer who negotiated
production the same day at a nearby glass-
works. London had over two dozen such works.
Seven years later a check made with new
chains by Ramsden gave a figure of 27,404.32'
and subsequent work was based on a mean
accepted as 27,4o4.2'. The margin of error
was of the order of 1 in 100,000. The
decaying pipes were eventually replaced by
gun barrels, and these stand to this day,
one in Hampton, the other near a boundary