north polar distances of the principal fixed stars. 63 
On the Southern Motion. 
In Table III. are given the North Polar distances of forty- 
six principal stars, from recent observations with the circle 
of the Observatory of T. C. Dublin, and also the North Polar 
distances of the same stars from the Catalogue of 1813* re- 
duced to 1823. -f 
The column of differences shows that there are none 
greater than what may be attributed to accidental circum- 
stances, especially when it is considered that the Catalogue 
of 1813 was formed from a small number of observations of 
each star. The mean difference =-J-o // ,2, whereas the 
mean difference of Mr. Pond’s Catalogues = -j- i",i. In 
this then our instruments are at variance. The discordance 
appears much more striking if we examine the differences 
that exist as to certain stars. It is from these, unless I am 
much mistaken, I shall be enabled to show the greater ex- 
actness of the Dublin instrument. But it may be useful to 
add a few remarks respecting the mean difference , to show 
there are reasons for supposing a constant error, which, being 
allowed for, would considerably reduce the above mean dif- 
ference of l",l. 
By Table I. it appears, the mean difference between the 
Dublin Catalogue of 1813, and the Greenwich Standard 
Catalogue of 1813 = -J- o",47. The mean difference between 
* Trans. R. I. Academy, Vol. 12, p. 69. 
t To the Catalogue which was published in the Journal of Science, October, 
1822, have been since added several stars, viz. a. Persei, Rigel, « Hydrae, 2 « Librae, 
as Herculis, and a. Pegasi. In that Catalogue, the mean difference from that of 1813 
was exactly o",o. 
