163 
A comparison haying been made between the quantity of rain which fell 
in two places in London, about a mile distant from one another, it was found 
that the rain in one of them constantly exceeded that in the other, not only 
every month, but almost every time that it rained. 
The apparatus used in each of them was very exact, both being made by 
the same artist; and upon examining every probable cause, this unexpected 
variation did not appear to be owing to any mistake, but to the constant effect 
of some circumstance, which not being supposed to be of any moment, had 
never been attended to. The rain-gauge in one of these places was fixed so 
high as to rise above all the neighbouring ehimnies; the other was consi¬ 
derably below them; and there appeared reason to believe, that the difference 
of the quantity of rain in these two places was owing to this difference in the 
placing of the vessel in which it was received. A funnel was therefore placed 
above the highest ehimnies, and another upon the ground of the garden belong¬ 
ing to the same house, and there were found the same difference between these 
two, which there had been between them, when placed at similar heights in 
different parts of the town. After this fact was sufficiently ascertained, it was 
thought proper to try, whether the difference would be greater at a much 
greater height; and a rain-gauge was therefore placed upon the square parts 
of the roof of Westminster Abbey, being at such a distance from the western 
towers as probably to be very little affected by them, and being much higher 
than any other neighbouring buildings. 
Here the quantity of rain was observed for a twelvemonth, the rain being 
measured at the end of every month, and care being taken, that none should 
evaporate, by passing a very long tube of the funnel into a bottle through a 
cork, to which it was exactly fitted. The tube went down very near to the 
bottom of the bottle, and therefore the rain, which fell into it, would soon 
rise above the end of the tube, so that the water was no where open to the 
air except for the small space of the area of the tube: and by trial it was 
found, that there was no sensible evaporation through the tube thus fitted up. 
The following table will shew the result of these observations. 
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