59 
especially the week ending the 28th, when the mean was only 34.8. 
Considerable oscillation was recorded in the barometric pressure 
throughout the month ; the most sudden variation was a fall of 
.811 in. in fifteen hours, from 29.410 at 9 p.m. the 28th, to 
28.599 at noon the 29th ; this unusually low pressure was 
followed by a strong S.W. gale from 2 p.m. to midnight on 
the 29th; 1.01 in. of rain fell on the same day, causing the 
monthly fall to exceed the average by .056. The year closed 
with a month of almost unprecedented cold weather; Mr. Glaisher 
says, that the mean temperature for December was the lowest 
recorded at Greenwich since 1846, and that only six other instances 
of so low a mean temperature in December has been recorded in 
the last hundred years. The mean temperature of the week ending 
the 5th, and four following weeks were, 36 9, 37.5, 33.7, 28.3, and 
22.1; and the mean for the month only 31.9. During the last 
seventeen days the thermometer did not rise above 38.0, and on 
the last six not above 32.0. Frosts occurred on twenty-three 
nights, the minimum on the night of the 29th was twenty-two 
degrees below freezing ; and tho maximum on the 31st was nine 
degrees below. The first fortnight was especially remarkable for 
tho great variation in the barometric pressure ; at 10 a.m. the 1st 
it registered 29.243 ; increased .847 in. in the next forty-eight 
hours, decreased to 29.206 on the 6th, followed by a rise to 29.890 
at 9 p.m. the 7th, attended by a W.S.Wh gale. The following 
unusual oscillations were also recorded : On the 8th from 29.730 
at 10 a.m. to 28.815 at 10 p.m., a fall of .915 in twelve hours • 
from 28.883 at 10 a.m. the 9th to 29.695 at 10 a.m the 1 0th, a 
rise of .812 in twenty-four hours; and from 29.664 at 9 p.m. the 
10th, to 28.648 at 9 p.m. the 11th, a fall of 1.016 in twenty-four 
hours, followed by an unbroken rise to thirty inches on the loth. 
The chief gale during this period was from the N.W. on the 9th, 
when the velocity of the wind was 264 miles in twelve hours. 
The rainfall for December was .177 in excess of the average ; the 
total fall for the year, 18.95 in., was 4.63 in. deficient. 
Note. —No barometric observations were taken from the 18th to the 28th 
of August ; the pressure during this period was high, the mean therefore 
of the observations recorded is below the proper average, probably by 
about .150 in. 
