ArrRACTION IN THE CASE OF THE ENGEISH ARC. 
45 
more accurate data. But the calculation may be useful to illustrate the use of the 
formula. 
22- If a meridian line be drawn about thirty miles west of Burleigh Moor, the 
resultant attraction on that place of the portion of the British Isles to the west of 
that line will be due west or nearly so, whatever be its amount, which is doubtless 
smali. For the mountain region of Cumberland and Westmoreland lies due west; 
and those of Scotland and Wales lie at about the same bearing north and south of west, 
and therefore taking their mass to be about the same their resultant attraction will 
be west. The attraction too of the level country west of the line laid down, and of 
the table on which the mountain regions rest, will be about west. So that we may 
conclude that the part of the land which is effective in deflecting the plumb-line at 
Burleigh Moor in the plane of the meridian is that portion which lies east of the 
line. 
This tract of country I divide into four portions. A, B, C, D, as marked in the Plate. 
The small irregular portions a and b on opposite sides of the station I suppose to 
counteract each other. The station itself I suppose to be in the centre of a neutral 
parallelogram, of which the north and east sides are the average line of sea cliff in 
that neighbourhood. The distances of these cliffs 1 put down as 3 and 10 miles. 
This I deduce merely from the map in the account of the Survey : it is in these 
assumptions regaiding the parts nearest the station that the chief sources of error 
will lie in the present calculation, from insufficient data. The portion to the west of 
the station, marked c, will have no effect in the direction of the meridian. 
The mass A will produce a deflection northward ; the other masses, southward. 
The average heights I take to be 505, 628, 448, 394 feet above the sea-level. 
23. The following Table is formed from the formula given in art. 16, according to 
the Rule laid down in art. 20. 
