4 9 ° An Account of the Measurement 
sector's limb was not got into that of the meridian. Such an 
idea, however, can scarcely be entertained, after a careful exa- 
mination of the several observations, and a due attention to the 
means by which the instrument was made to assume its right 
position. Perhaps, also, I should not fail to observe, in this 
place, that although the instrument was always brought into the 
plane of each meridian by means of the telescope attached to 
the side of the great tube, and the azimuth circle, yet, having 
two good chronometers in my possession, I repeatedly verified 
the truth of the sector’s position, by observing the transits of 
two stars, north and south of the zenith, at the greatest distances 
my arc would admit of. But, to return, if there be an error in the 
amplitude of the total arc, from a deflection of the plumb-line at 
either of the stations, it is not probable that any such deflection 
existed at Dunnose; as the deviation of it towards the north, 
from a deficiency of matter towards the channel, would tend to 
diminish the inequality between the lengths of the two degrees. 
This will be evident, on consideration. I am therefore disposed 
to believe that the plumb-line was drawn towards the south, 
from the action of matter, both at the northern extremity of the 
arc and at Arbury Hill, but more particularly at the first- 
mentioned station. If this were partly the case, and both Dun- 
nose and Arbury Hill were free from any such prevailing cause, 
the total arc must be too great, if taken at 2° 50' 23", 38, by 
about 8", nearly answering to 2" on each degree. A deviation of 
8" from the true vertical, is a large quantity ; nor can the cause 
of it be assigned, unless it be also supposed, that the matter pro- 
ducing that deflection extends in a southern direction beyond 
Arbury Hill. If the error, though not probable, as above ob- 
served, be supposed to exist at Dunnose, it must amount to 
