18 
Another important circumstance is to be taken into account, that 
ihe same irregularity of refraction takes place in four observations of 
ihe same day ; this therefore reduces the above number of observa- 
tions to the number of days, as far as refraction is concerned. ‘T'his 
must have considerable effect as to the values of x,2, p, and e, in the 
four resulting equations. In consequence it is my intention in future, 
as to this star, to endeavour to increase the number of days of ob- 
servation, and take only two observations on the same day. 
In my paper in the Phil. Trans. 1821, I mentioned a difficulty, as 
io stars of considerable zenith distance, that occurred respecting the 
internal and external Thermometer, and stated my reasons for ad- 
hering to the use of the internal Thermometer. In the present case, 
it seemed desirable to examine the effects of computing the refraction 
by the external Thermometer, and the importance of the result ap- 
peared sufficient to compensate for the length of the calculation. 
The last terms of the above four equations were changed into 
1. +143,86 
2. —44,8546 
3. — 60,8347 
4, — 168,6283 
Then 
z= +0”’,9860 
p= +1,4218 
r= +0,7689 
e= —0,2921 
Nothing is here gained as to the value of z, and therefore the 
use of the internal Thermometer cannot have occasioned the 
difficulty. 
In consequence of these values of z, for the present it appears 
better to suspend all conclusions as to the values of p and the con- 
