[ III ] 
ways in the proper part of the horizon-glafs. When- 
the Sun is near the horizon, the line going from the 
eye to the Sun will not be far removed from the axis 
of vilion ; and confequently the principal motion of 
the quadrant will be performed on the axis of vilion, 
and the part of the motion made on the vertical axis 
will be but fmall. On the contrary, when the Sun 
is near the zenith, the line going to the Sun is not 
far removed from a vertical line, and confequently 
the principal motion of the quadrant will be per- 
formed on a vertical axis, by the obferver’s turning 
bimfeif about, and the part of the motion made on 
the axis of vilion will be but fmall. In intermediate 
altitudes of the Sun, the motions of the quadrant 
on the axis of vilion and on a vertical axis will be 
more equally divided. Hence appears the reafon 
of the method ufed by the bell obfervers in taking; 
the Sun’s altitude when near the zenith by holding 
the quadrant vertical and turning about upon the 
heel, and the defedls of the rules that have been 
commonly given for obferving altitudes in other cafes.. 
As it may conduce to the fetting this matter in- 
a Hill clearer light, I lhall here defcribe in order 
the feveral motions that will be given to the reflected 
image, by turning the quadrant about upon the 
axis of vilion, a vertical axis, or the line drawn, from-, 
the eye to the Sun, fucceffively. 
I. If the quadrant is turned about upon the- 
axis of vifion, the fame being dire&ed to the 
point of the horizon exadtly beneath or oppo- 
fite the Sun, the image of the Sun will move- 
from, right to left, or from left to right, acrofs 
