and the Weather which preceded and followed. 543 
respect to the leafing of trees. At Swaffham Bulbeck, the 
whitethorn was seen in leaf by the 20th of March, and the 
horsechestnut by the 23d; it being, in each case, only five 
days later than in the season following the unparalleled mild 
winter of 1821-22: whilst a large number of other trees began 
to exhibit their foliage towards the end of that month and 
the beginning of the next; many of which, as the lime, elm, 
birch, beech, and hornbeam, were even several days earlier 
in that respect than the same trees in the year above-men- 
tioned. 
There can be little doubt that this forward state of vege- 
tation was, latterly, in a great measure owing to the unusually 
hot weather which prevailed during the last week in March. 
The former part of that month, indeed, may, with the excep- 
tion of a very few days, be said to have been mild; but upon 
the 25th the thermometer rose to 60°, and from that time to 
the 30th the temperature was, perhaps, higher than on any 
six consecutive days before remembered at so early a period 
of the year. I regret that absence from home prevented me 
from noticing the exact maximum degree of heat on the 26th 
and 27th; but so late in the day as 5 p.m. I found the ther- 
mometer, on each occasion, standing in the shade as high as 
67°; and on the two following days the same instrument, in 
a situation where it was wholly out of the reach of radiation, 
rose to 66° and 69° respectively. On the 30th it fell again to 
60°. The weather during these six days was extremely fine, 
and uniformly followed after sunset by calm bright evenings, 
which caused at night, as is usual under such circumstances, 
a considerable radiation of heat from the surface of the earth. 
To try the extent of this, as well as the force of solar radiation 
during the day, on the evening of the 27th I placed a small 
thermometer, having a naked bulb, upon short grass, in a 
situation where it was fully exposed to the open sky. B 
7 o’clock this thermometer had fallen to 40°, and by 9 o’clock 
to 38°, having the bulb and stem of the instrument covered 
with dew. At the time of this last observation the tempera- 
ture of the air was 49°5°, indicating a difference of 11°5°.* I 
again examined this thermometer at 6 o’clock on the following 
morning, when J found it standing at 30°, and firmly held to 
the grass by hoar frost; but the temperature of the air had 
likewise fallen as low as 37°; so that the difference between 
them, or the amount of terrestrial radiation, was at this time 
* Daniel states the maximum force of terrestrial radiation ever observed 
by him in this month to be 10 degrees. (Meteorological Essays, p. 230.) 
NN 4 
