342 Analysis of Scientific Books. 
night above the aflernoon +.010 inch. ‘The means of the monthly 
observations presented but one or two exceptions to the fail in the 
middle of the day, or to the rise from afternoon to night ; but the rise 
from night to morning was not quite so constant. 
With regard to the dew-point, four observations were made daily, 
including the observation of the minimum temperature, which con- 
stantly falls a few degrees below the term of precipitation taken in the 
day. From morning to afternoon it was found to rise but 0.3 of a 
degree; from afternoon to night it fell 0.9 of a degree; and below 
this again, the minimum temperature was 2.7. Tle mean was calcu- 
lated from this and the afternoon observation. 
The temperature of the air was found to vary in the twenty-four 
hours from 569.1, its mean maximum to 4.2°.5 its mean minimum. 
“The mean temperature of a climate,” says our author, ‘ is ge- 
nerally regarded as made up of the average impression of the sun due 
to its latitude upon the surface of the globe. The mean quantity of 
aqueous vapour must also be referable, finally, to the same principle. 
But there is another way of considering the subject more accurate in 
detail, though upon an average of years ending in the same conclu- 
sion: that is, to regard the mean temperature as made up of the tem- 
perature of different currents flowing from different points of the 
compass; and it will be necessary to my purpose to contemplate the 
atmosphere of vapour particularly, in this point of view. The medium 
dew-point 44°.5 is therefore made up of the following proportions of 
the means from eight points of the wind :— 
Oo 
87 North 40.1 — 133 North-east 40.7 
80 East 42.3 — 111 South-east 45.6 
70 South 48.7 — 225 South-west 48.6 
215 West 44,8 — 174 North-west 41.3 
“* Before I enter upon the consideration of the effect of the sun’s 
progress in declination, and the succession of the seasons, I shall en- 
deavour to point out the influence of the geographical situation of the 
island of Great Britain upon its aqueous atmosphere. The mean 
quantity of the vapour follows exactly the changes of the mean 
monthly temperature, that is to say, the dew-point rises and falls 
with the increase and the decrease of the heat. But the winds which 
transport the vapour, may be divided into two classes; namely, the 
Jand-winds which blow from off the great continent of Europe, and 
which comprise the north-east, the east, and south-east; and the sea- 
winds which blow from the great oceans which surround it on every 
other side, viz., the north, north-west, west, south-west, and south. 
In the former we may expect to find that the course of the mean 
temperature is exactly followed; for the sources of the vapour must 
be comparatively shallow streams, and reservoirs of water, whose 
temperature must soon adapt itself to that of the surrounding air. 
