482 Mr . Pond o« the parallax of 
tion, are u Aquilas, Arcturus, Capella, and a. Lyrae. Sirius is 
comparatively but seldom observed, from its vicinity to the 
horizon. As the observations of all the above stars give the 
same result, it will be sufficient to select one as an example. 
I have chosen « Aquilas. The annexed table contains 120 
observations of this star ; and the following remarks will, 
I trust, be thought sufficiently conclusive to establish the point 
in question. 
If a series of 12 results (obtained by 120 observations) be 
divided into two parts, first, according to the law of parallax, 
and next alternately, or in a manner perfectly accidental, then 
it so happens, that a greater difference is found in the latter 
or accidental mode of division, than in the former. From this 
it is evident, that the determination of the quantity of parallax 
is out of the power of the instrument to determine with this 
number of observations. The next question is, What are the 
limits within which parallax is restricted ? 
In examining several series of observations, I find that the 
result of 6 o observations, reduced to the equator, and taken 
accidentally, never differs from the more correct mean derived 
from 120 by more than o",oi of time, when reduced to the 
equator. 
If of 12 results taken as above, the 6 least be classed 
together, and compared with the six greatest, the error of 
either class will not exceed the double of this quantity, or 
o",02. It is therefore very highly improbable indeed, that 
an error of this magnitude should exist in a result deduced 
from 60 observations. 
Since, therefore, the results arranged according to the law 
of parallax should differ by rather more than half the double pa- 
rallax.! infer, that it is most highly improbable that the longer 
