north polar distances of the principal fixed stars. 77 
Two of the four stars above mentioned are /3 Tauri and 
Pollux. Mechain’s declination gives the predicted N. P. D. 
of 0 Tauri, conformable to Mr. Pond’s southern motion, who 
makes it only o'', 7, a quantity evidently too small to found 
an argument on ; besides, Mechain’s places of this star, de- 
duced at Paris and Montjoy, differ by i",8. 
Pollux also gives a southern motion, but Mr. Pond, finds 
the southern motion of this star only o",2. Also Mechain’s 
results as to Pollux are very discordant. 
Mechain’s declination of Sirius also seems to support the 
southern motion, but in this it is opposed by that of Piazzi. 
I shall conclude by mentioning a result recently obtained, 
that shows, in a remarkable manner, that the Dublin circle 
has been consistent with itself from the beginning, and has 
suffered no derangement. 
From 1809 to 1823, inclusive, thirteen summer solstices 
have been observed with the circle, for which, observations 
on eighty seven days have been made. I have investigated 
from these, the maximum of lunar nutation, and found it 
= 9", 60, which happens to be exactly what I have hitherto 
used for the Sun. I am induced, however, to give more 
weight to my result from the stars, viz. 9", 26*. The dif- 
ference is less than could have been expected from solar 
observations. It puts beyond all doubt the permanent state 
of the instrument. Had any circumstances taken place 
similar to those, of whatever nature they may be, by which 
the Greenwich instrument has shown so great a southern 
motion in certain stars, they must have given a very erro- 
neous quantity of lunar nutation. 
Philosophical Transactions, 1821. 
