44 
Documents 
used. 
Work involved. 
Absolute range. 
Monthly range. 
hlxtremes of 
IMonthly means. 
Seasonal range. 
The present work lias been based chiefly upon tlie annual 
tables published in the Y.P.S. reports, wliicb appear first in 
1841. These represent an amount of labour Avhieh it is not 
easy to appreciate. In 1844 Mr. John Ford speaks of having 
made 2000 observations of the barometer. The final value for 
the mean height of the barometer for the oO years is found by 
the use of at least 36,525 observations, double that number of 
calculations and half a million figures. 
PKESSURE* 
[Mr. Ford’s returns fup to 1873) were'corrected for temperature and capillarity, 
not for sea-level and instrumental error, O-Ooo and 0-004 respectively. 
Consequently 0'06 has been added in all cases previous to 1874.] 
This has ranged from 27‘777, on Dec. 8th, 1886, to o0‘99 on 
March 4th, 1854, an absolute extreme of 3‘21 inches. On no 
other occasion did it fall below 28 ins. [in Jan., 1843, it 
reached 28’05); once besides, in Feb., 1849, it just reached 
30’96. It had not been so high as 30’99 in the previous 25 
jmars.t The excessive ranges are in the winter months; 
3 08 ins. in Dec., 2‘84 in Jan. The least are in summer; 1’73 
in May, 1*53 in June, and 1*83 in July. As, on Nov. 24th, 
1886, just before the deep depression of Dec. 8th, the barometer 
had reached 30 693, we have a range in 14 days of 2*916 inches. 
In 1876 the barometer fell below 29 inches 5 times in March, 
once in April, and 6 times in December. In 1883 it fell from 
30'631 on Jan. 23rd to 28 630 on the 26th. 
Like the absolute extremes, so too the range of the means for 
each month is greatest in winter. Thus we find it to be 1*08 
in March, 0*92 in Jan. and 0 85 in Dec., but only 0*55 in May, 
0 48, 0*51 and 0*53 in June, July and August. For the whole 
year the means have ranged from 29*70 in 1872 to 30*00 in 
1887. Finally, the mean lor the whole 50-year period varies 
but little from month to month, and rather irregularly. The 
maximum is 29*958 in June, from which it drops to 29*844 in 
October, a range of only 0*114, with a menu height of 29*905. 
A rise in Sept., from July and Aug., a hill in Jan., from Dec. 
and Nov., and in March and April, from Feb., produce the 
irregularities. 
* Plates II. and III. represent graphically most of the points considered here. 
tReferences to the observations from 183i-40 often occur in the reports and 
enable us to glean considerable information concerning that decade. 
