OF THE MAGNETIC DECLINATION AT POINT BAEROW. 
499 
being \isible to seaward. On the 21st of December the instruments were replaced : 
the water had come within 6 inches of the top of the pedestal.” 
On the 1st of June, 1853, the observatory was unroofed, on account of the increasing'' 
heat of the w eather, and on the 22nd of June the hourly observations were discontinued, 
all hands being required to assist in the preparations to meet the vessel at Port Clarence 
which brought the annual supply of provisions. The observations were again resumed 
on the 12th of October, 1853, with the same instruments, placed as in the preceding 
year; and were continued to the 30th of June, 1854, when the ‘ Plover’ finally quitted 
Point Barrow on her return to England. 
The hourly observations of the declination at Point Barrow consist therefore of two 
series: the first of eight months, fi:om November 1852 to June 1853 ; and the second of 
nine months, from October 1853 to June 1854; making, together, seventeen months. 
The observations were arranged in monthly tables, of the same form as that adopted at 
the Colonial Observatories, having the monthly, daily and hourly means computed from 
the whole of the observations without any omissions on account of excessive disturb- 
ance. The record was kept in scale-divisions, the value of a scale-division being 2''287. 
In this state the Tables were received at Woolwich. 
For the purpose of separating the disturbances of largest amount from the rest of the 
observations, ten scale-divisions above or below the normal at the same hour in the same 
month were adopted as a suitable measure of what should be regarded as a large disturb- 
ance ; the corresponding arc value is 22'’87. The number of disturbed observations thus 
separated was 907 in 1852-53, and 914 in 1853-54. The whole number of observations 
was 4659 in 1852-53, and 5413 in 1853-54: making, together, 10,072, of which 1821 
differed from their respective normals by an amount equalling or exceeding 22'-87 ; being 
between one-fifth and one-sixth of the whole number. The aggregate amount of disturb- 
ance, counted from the respective normals, was 44156'’0 in 1852-53, and 47388'-2 in 
1853—54; of which, in 1852-53, 24823'*0 was easterly, and 19333'‘0 westerly disturb- 
ance; and in 1853-54, 31935'T easterly, and 15453'T westerly disturbance. The sum 
of the easterly values in the seventeen months was 56758'T, and of the westerly values, 
34786'T. In both series, therefore, the easterly disturbances preponderated ; in 1852-53 
in the proportion of 1-28 to 1, and in 1853-54 of 2‘07 to 1 ; in both, conjointly, in the 
proportion of 1‘63 to 1. Consequently the influence of the disturbances at Point Barrow 
was to occasion a small mean deflection of the needle toAvards the east, thus slightly 
increasing the easterly declination. 
In the following Table the aggregate values of the disturbances in the seventeen 
months are distributed into the hours of thefr occurrence ; and the ratios are given Avhich 
the values at the different hours bear to the mean of all the hours, or, in other words, 
to the aggregate values di Aided by 24. 
3 T 2 
