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 deg. or a little above it, but that the actual mean varies from 46 deg.-48 deg. on the Chiltern Hills to 48 deg.-50 deg. 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.

Hertfordshire is hilly though not mountainous, a great extent of its surface being considerably elevated above sea-level, with a general south-easterly inclination; it has a dry soil; is well watered with numerous rivers of clear water—­already enumerated—­chiefly derived from springs in the Chalk; is well but not too densely wooded; and its atmosphere is not contaminated by manufacturing towns.  It thus maintains the reputation for salubrity which it gained more than three centuries ago, our earliest county historian, Norden, remarking on the “salutarie” nature of the “aire”.

Observations taken at the following meteorological stations during the twelve years 1887 to 1898 have been printed annually in the Transactions of the Hertfordshire Natural History Society, and a brief summary of some of the chief results will here be given.

Royston (London Road):  lat. 52 deg. 2’ 34’’ N.; long. 0 deg. 1’ 8’’ W.; alt. 301 feet; observer, the late Hale Wortham, F.R.Met.Soc.

Berkhampstead (Rosebank):  lat. 51 deg. 45’ 40’’ N.; long. 0 deg. 33’ 30’’ W.; alt. 400 feet; observer, Edward Mawley, F.R.Met.Soc.

St. Albans (The Grange):  lat. 51 deg. 45’ 9’’ N.; long. 0 deg. 20’ 7’’ W.; alt. 380 feet; observer, John Hopkinson, Assoc.Inst.C.E.

Bennington (Bennington House):  lat. 51 deg. 53’ 45’’ N.; long. 0 deg. 20’ 7’’ W.; alt. 407 feet; observer, Rev. Dr. Parker, F.R.Met.Soc.

New Barnet (Gas Works):  lat. 51 deg. 38’ 5’’ N.; long. 0 deg. 10’ 15’’ W.; alt. 212 feet; observer, T. H. Martin, M.Inst.C.E.

1. Temperature.—­The mean temperature of Hertfordshire, as deduced from the above observations, is 48.3 deg..  It has varied from 47.0 deg. in 1887 to 50.2 deg. in 1898.  The mean daily range is 15.9 deg..  It was the least (14.2 deg.) in 1888, and the greatest (18.1 deg.) in 1893.  The mean temperature of the seasons is as follows:  spring 46.6 deg., summer 60.2 deg., autumn 49.2 deg., winter 37.2 deg..  The warmest month is July, with a mean temperature of 61.0 deg.; the coldest is January, with a mean of 36.1 deg..  August is very little colder than July.  In these two months only has the temperature never been below freezing-point (32 deg.).  In December and January only has it never exceeded 62 deg..  It increases most rapidly during the month of May, and decreases most rapidly during September and October.