XXI. 
A NATURALIST’S CALENDAR FOR THE NORTHERN BORDER 
OF HERTFORDSHIRE. 
By H. George Fordham, F.G.S. 
Read at Watford , 1 9th April , 1887. 
From observation of the phenomena given below during the ten 
years period 1877-86, I have been able to construct a Naturalist’s 
Calendar for a district lying on the extreme northern border of 
Hertfordshire, and embracing the most southerly part of Cam¬ 
bridgeshire. Some of the phenomena have, unfortunately, not 
been observed in every year throughout the whole period, but on 
the whole the mean dates given in the Calendar may be taken to be 
fairly trustworthy. 
In three columns are given the earliest, latest, and mean dates of 
occurrence of the various phenomena, and, in a fourth, for the 
purpose of comparison, the mean of the earliest recorded dates for 
Hertfordshire for the ten years 1876-85, as published in the Trans¬ 
actions of this Society, Yol. IV, p. 93. 
It will be seen that there is, as would be expected, a well- 
marked difference, varying from 1 to 28 days (the mean date being 
the same, however, in one instance), between the mean dates up 
to the end of July ; Odsey being later than the mean of the earliest 
dates recorded anywhere in the county by an average (in the months 
of January to July) of 7 *9 days. The autumn observations are too 
few to rely upon, but they appear to indicate the earlier southern 
movement of the summer migrants from the north of Herts than 
from the county generally. 
As phenological observations are now generally recorded by 
reference to the day of the year, and not of the month, I have 
inserted in all cases the day of the year, in order to facilitate com¬ 
parison with other records, retaining at the same time the day of 
the month, as more readily understood by those who are not in the 
habit of referring to the former method of computing. 
The numbers in parenthesis in the first column are those used in 
the Royal Meteorological Society’s list of species recommended for 
observation. 
Particulars of Locaeity. 
Place : Odsey. Counties : Hertfordshire and Cambridgeshire 
(borders of). Longitude : 0° 6' 41" W. Latitude : 52° V 28" N. 
Area of observation : a radius of 2 miles. 
Elevation above sea: 150-500 feet ( Odsey 263 feet). 
Geology: Chalk, with patches of boulder-clay and gravel. 
Natural features: open arable fields and small plantations (very 
little pasture ; no mountain , swamp , or moor). 
Rainfall: mean of 10 years , 1877-86, 23*53 inches; highest in 
these ten years , 28*24 ins. (1879) ; lowest , 16*15 ins. (1884); mean 
number of wet days, 174; highest , 193 (1877); lowest , 142 (1884). 
VOL. IV.—PART VII. 13 
