5 
cause should occasion the instrument to shew deviations explained 
by parallax which did not actually exist, it should not derange the 
solar nutation, and cause the result of an investigation of its quan- 
tity to turn out quite erroneous. , 
This method of investigation, which I have applied to several stars, 
has produced most satisfactory results. 
There will not, I conceive, remain the smallest doubt with any 
one, who examines the processes which have been used, that the ob- 
servations have ascertained the quantities of parallax, with consi- 
derable exactness, of the stars « Lyre, « Cygni, and Arcturus, and 
that the parallaxes of y Draconis and 7 Urse Majoris are extremely 
small. That y Draconis is at least seven or eight times more distant 
than a Lyre. 
The application of the same method to # Aquile and a Ophiuchi 
has shewn, that the conclusions formerly deduced from the obser- 
vations of these stars cannot be depended on. There appear reasons 
for supposing, that the parallax of these stars may be considerable ; 
but, for the present, Iam willing to leave the matter entirely in 
doubt. The great zenith distances of these stars appear to have 
been attended with an irregularity of refraction, which has mixed 
itself with the other changes of place; as will be more particularly 
considered, when the computations as to « Aquile are stated. 
The results of this enquiry are connected with several important 
"points in practical astronomy. It has not before been altempted, 
as far as I know, to ascertain by actual observation the quantity of 
solar nutation. The precision with which this equation, mixed up 
with the other-various complicated apparent motions, has been 
ascertained, shews an advanced state of instruments that formerly 
would scarcely have been hoped for.—Newton, who pointed out 
from theory the existence of the solar nutation, (the lunar so much 
