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XIV. 
THE CLIMATE OF HERTFORDSHIRE, 
DEDUCED FROM METEOROLOGICAL OBSERVATIONS TAKEN 
DURING THE TWELVE YEARS 1887-1898. 
By John Hopkinson, F.L.S., F.Gr.S., F.R.Met.Soc., Assoc.Inst.C.E. 
Read at Watford , 2 5th March , 1902. 
PLATE VII. 
Climate has been defined by Dr. H. R. Mill as “the normal or 
average condition of meteorological phenomena at a given place,” 
or in other words “the average weather of a place,” the former 
being its theoretical and the latter its practical aspect.* By an 
inspection of maps in a meteorological atlas such as that issued by 
the Meteorological Council,! or the fine ‘ Atlas of Meteorology ’ 
edited by Dr. Buchan, { a general idea may be gained of the two chief 
elements of climate—temperature and rainfall,—in the former work 
for any part of the British Isles, and in the latter for any part of the 
world. From this work, the only atlas which gives the monthly 
rainfall, it appears that the mean annual temperature of that part 
of England in which Hertfordshire is situated, if reduced to sea- 
level (that is, the theoretical mean for its latitude and position with 
regard to the sea-coast of England), would be 50° or a little above 
it, but that the actual mean varies from 46°-48° on the Cbiltern 
Hills in the north-west to 48°- 50° in the rest and much the greater 
part of the county ; also that the mean annual rainfall is between 
25 and 30 inches, the larger amount being approached in the vicinity 
of the Chilterns only. 
In ascertaining from an atlas the average temperature and rain¬ 
fall, which are the only climatic elements usually given, we have 
the advantage of easy comparison with the same elements of the 
climate of other parts of the British Islands, of Europe, or of the 
world; but climate is too complex a phenomenon for any definite 
idea of the average weather of Hertfordshire (its practical aspect) 
to be thus formed. Not only have we to consider the temperature, 
rainfall, humidity of the air, amount of cloud and sunshine, and 
the force and direction of the wind, but also the elevation of the 
surface, the nature of the soil, the extent of water, of woods, of 
barren heaths and cultivated land, and the presence or absence of 
manufacturing towns or districts. 
Hertfordshire is hilly, though not mountainous, a great extent 
of its surface being at a considerable elevation above sea-level, 
especially towards the north-west, the general inclination being 
south-easterly; it has a dry soil, is well watered with numerous 
* “Climate and the Effects of Climate”: ‘Quart. Journ. Royal Meteorol. 
Soc.,’ vol. xxvii, p. 172. 1901. 
t ‘ Meteorological Atlas of the British Isles.’ 4to. 1883. 
X Bartholomew’s ‘ Physical Atlas,’ vol. iii. Folio. 1899. 
VOL. XI. —PART IV. 
