on the Planet Mars. 266 
#he equator, was then in the following quadrant. The mea- 
fure of both the {pots on June the 25th, 1781, is {till more 
to be depended on, as giving us very nearly the pofition of the 
true pole; for it appears evident from the phaznomena of the 
bright north-polar {pot in fig. 26. that that fpot was in the 
meridian when the meafure was taken, while the fouthern {pot 
was in the preceding quadrant near its greateft limit. Now, 
fince an angle at the circumference of a circle is but half the 
angle at the center, when the arches which fubtend thefe 
angles are equal, the correction neceflary to be applied to the 
meafure taken through the two fpots will be but one half of 
the correction which would have been requifite had it been 
taken through the center; therefore, in order to reduce this 
to the condition of the former, we may fuppofe it to have been. 
taken through the center of Mars when the {pot was only 30, or 
1 5odegrees from the meridian. It is alfo neceffary to add 1°54’ to. 
the angle of July 15, which it would have meafured more had 
the planets remained where they were June 25. ‘This done,. 
we may have the polar diftance of the center of the fpot as 
before. Half the fum of the.fines (of 231° 38’ and 150°) to 
tadius, as 50’ (half the difference between 74° 32’ and 76° 12’) 
to a fourth number, which is 1° 18’. 
I fhould obferve here, that the meafures of the angle of pofi- 
tion would be too large before the {pot came to the meridian, 
and too {mall afterwards, the axis of Mars being fouth pre~ 
ceding; whereas, in fig. 28. they would be too {mall before,, 
and too large after, the meridian paflage, the pole being fouth: 
following. 
 ‘Thefe two obfervations arranged as thofe in the fourth table,, 
and reduced to the time. of the 25th of June, will ftand as. 
follows. 
| TABLE 
