496 
Dr. Brinkley's remarks on 
The readings from which these are deduced are given in 
my paper on solar nutation, printed for the XIVth Volume 
of the Transactions of the Royal Irish Academy, and of which 
paper copies have been for some time in the hands of several 
persons. 
In part(i), the second column marked WL (meaning 
face of the circle west and left hand microscope ) contains 
the differences between the bottom microscope and the left 
hand microscope for each day. The column marked WR 
contains the difference between the bottom and right hand 
microscope. The fourth column, WM, contains the mean 
of these differences for each day. These second and third 
columns show a great steadiness during such a length of 
time. There are no sudden changes, such as we meet with 
in the Greenwich circle. Nothing, I conceive, can be more 
remarkable than the contrast in this respect between the two 
instruments. In the Dublin circle, when a change appears 
to take place, it comes on gradually. 
From the construction and manner in which the Dublin 
circle is supported, it is to be expected that changes may take 
place of the relative positions of the two microscopes to the 
bottom microscope, while the mean of the two microscopes 
will still preserve the same relation to the bottom micro- 
scopes. This is shown most satisfactorily in column 4, 
marked WM. 
Part (2) contains the comparison of the microscopes when 
the face of the circle was east. The same consistency appear 
here as when the face was west. No stronger proof of the 
excellence of the Dublin instrument can be required than is 
exhibited by the columns WM and EM. 
