? (way Reid (i) 
. ve 
234 Mr. Herscuer’s Obfervations 
after they have been given in the order they were 2 made, it 
will. be eafy to fhew, by a few deductions from them, that my. 
theory of this planet is fupported by facts which will fuffi- 
ciently authorife the conclufions I have drawn from them. For 
the fake of better order and perfpicuity, however, I fhall treat 
each fubject apart, and begin with the remarkable appearances 
about the polar regions. The obfervations on them were made 
with a view to the fituation and inclination of the axis of 
Mars; for to determine thefe we cannot conveniently ufe the 
{pots on its furface, in the manner which is practifed on the 
fun. The quantities to be meafured are fo fmall, and 
the obfervations of the center of Mars fo precarious, and 
attended with fuch difficulties (fince an error of only a few 
feconds would be fatal) that we mutt have recourfe to other 
methods. 
When I found that the poles of Mars were diftinguifhed with 
remarkable luminous {pots*, it occurred to me, that we might 
obtain a good theory for fettling the inclination and nodes of 
that planet’s axis, by meafures taken of the fituation of thofe 
fpots. But, not to proceed upon grounds that wanted confir- 
mation, it became neceffary to determine by obfervation, how 
far thefe polar fpots might be depended upon as permanent ; 
and in what latitude of the globe of Mars they were fituated ; 
for, if they fhould either be changeable, or not be at the very 
poles, we might be led into great miftakes by overlooking thefe 
circumftances. The. following obfervations will affift us in 
the inveftigation of thefe preliminary points. 
* A bright {pot near the fouthern pole, appearing like a polar zone, has alfo 
been obferved by M. MaRazpii See Dr. Smirn’s Optics, § 1094. ° 
37773 
