Trigonometrical Survey. 48 1 
that the joints had not rusted while the chains remained in 
the Tower ; but to prevent this, care had been taken to de- 
posite them in a dry place, being afterwards frequently exa- 
mined and oiled. 
Thus concluded the measurement of this base, in which it 
is certain that great pains were taken to produce an accurate 
result ; and we are not without hopes, that the many obstacles 
which offered themselves have been surmounted with success ; 
but this is left to the decision of the candid and intelligent 
reader. 
The following table contains the particulars of this opera- 
tion. The first column showing the number of hypotenuses ; 
the second, that of the chains in each hypotenuse ; the third, 
the observed angles of elevation or depression given to the 
nearest 10"; the fourth and fifth, the perpendiculars answer- 
ing to the elevations and depressions ; the sixth, the reduction 
of the hypotenuses to the horizontal lines, or the versed sines 
of the elevations and depressions to the hypotenuses as radii ; 
the seventh and eighth, the perpendicular distance between 
the termination and beginning of any two hypotenuses when 
a new direction was commenced above or below. 
