20 
NATURAL HISTORY 
on four days ; feven degrees on five days ; eight degrees on three 
days ; nine degrees on one day ; and one day it varied twelve de- 
grees; viz/ on the 2 2d of July : whereas on the fame day it varied 
with me at Ludgvan but four degrees. 
From the following table it will appear how much greater the 
variation of the Thermometer was at London than in Cornwall in 
the Summer, Autumn, and fpring months, 1756 and 1757. 
Variation of Farenheit’s Mercurial Thermometer. 
JULY 1756. 
In Cornwall. In London. 
Degrees. Days. Degrees. Days. 
OCTOBER 
1756. 
In Cornwall. 
In London. 
Degrees, 
Days. 
Degrees. 
Days. 
1 7- 
r 3 
1 
'4 
2 ( g 
) 1 
2 
'■O 
9 
3 J 
v 
3 
4 
QJ 
4 
7 
4 J 
c I 
5 
M 
3 
No variation 4 
6 
3 
7 ' 
X 
MARC 
In Cornwall. 
Degrees. 
1 
2 
3 
4 
No variation 
Higher in the ) 
Morning than f 
at Night J 
H 1757. 
In London. 
Degrees. 
I " 
r 
2 
3 
4 
"7 6 
S 
a 
6 
>M< 
a 
7 
& 
10 
0 _ 
b 
Days. 
1 
5 
7 
9 
2 
2 
2 
The feveral degrees multiplied by the days will Ihew the differ- 
ence. The reafon of this greater variation of the Thermometer at 
London than in Cornwall is, chiefly, that the reflection of the fun- 
beams from a trad of land which has no large portion of the fea near 
it, makes it hotter at noon, and confequently the quickfilver rifes 
higher than in Cornwall and in fmall iflands, where there being a 
greater quantity of fea than of land, they want this additional heat 
and the quickfilver rifes but a fmall matter; on the other hand the 
ceafing of this refledion in the inland-parts by the coming on of 
night, makes the Mercury fink in proportion ; whereas in Cornwall, 
as the noon is not hot, the night varies not fo much from the day, 
efpecially if the day be cloudy, when I find the Mercury at eight 
or nine o’clock p. m. almofl: as high as at noon, and the general 
difference at a medium, but one degree. The greateft difference 
in the height of the Mercury in Cornwall therefore, is between eight 
at night and four or five in the morning. 
It may not be amifs here to obferve how different the weather 
is now and then in climates not very diftant : In the year 1751 we 
had a very rainy fummer throughout England, fcarce two days 
palling without frequent fhowers, and the Mercury in the Baro- 
meter very unfettled ; in three days Ipace varying generally ~ 
parts of an inch. At the fame time, in Italy prevailed an ex- 
traordinary drought ; the accounts from Parma, dated July 17, 
running thus, “ Publick prayers are ftill continued in all our 
d According to the account publiflied at London of Mr. Ayfcough’s obfervaticns. 
churches, 
