[Illustration: GRAND JUNCTION CANAL AT TRING
_The highest water level in England_]

_The Grand Junction Canal_ is largely utilised by barges traversing the
W. of Hertfordshire. It is conspicuous at Rickmansworth, Boxmoor, and
Berkhampstead; it enters Bedfordshire near Marsworth Reservoir.

_The New River_ was constructed by Sir Hugh Myddelton, a London
goldsmith, in 1609-13, and is largely fed by springs at Chadwell near
Hertford. Its course in Hertfordshire is mostly close to and parallel
with that of the Lea. The New River caused the financial ruin of its
projector; one of its shares is now worth a large fortune. The whole
story of this undertaking is very interesting; but as the New River was
cut in order to bring water to London that story belongs to a volume on
Middlesex.


III. CLIMATE

The chief elements of climate are temperature and rainfall. A general
idea of the mean temperature and rainfall of Hertfordshire, both monthly
and annual, may be gained from an inspection of Bartholomew's _Atlas of
Meteorology_ (1899). From that work it appears that the mean annual
temperature of the county, if reduced to sea-level (that is, the
theoretical mean for its position) would be 50° or a little above it,
but that the actual mean varies from 46°-48° on the Chiltern Hills to
48°-50° in the rest and much the greater part of Hertfordshire; also
that the mean annual rainfall is between 25 and 30 inches, the latter
amount only being approached towards the Chilterns. Thus altitude is
seen to have a great effect on both these elements of climate.