4 
on the Planet Mars.. — ase 
Of ihe direction or nodes .of the.axis of Mars, its inclination to- 
the ecliptic, and the angle of that planet’s equator with is own 
orbit. . | 
From the foregoing article we may gather, that the bright« 
polar {pots on Mars are the moft convenient objects for deter- 
mining the fituation of the axis of this planet; I fhall there-- 
fore colle@,.in oneview, all the meafures I have taken. of thefe - 
{pots for that purpofe. Before I conftruéted a micrometer: for. 
taking the angle of pofition, I ufed to draw a_line through the 
figure delineated of Mars to reprefent the parallel of declina-- 
tion.;.in a. few of my firft obfervations, therefore,.I can only - 
take the fituation of the polar {pots from fuch drawings, and - 
of confequence no great accuracy in the angles, as tothe exac- 
number.of degrees, can be expected. 
1777, Aprilr7. 7h. 50’. A line drawn. through the middle of» 
the two bright polar fpots @ and 4, fig. 1. makes an: 
angle of about 63°, with a parallel of declination: 
AB; the fouthern {pot preceding andthe northern. 
following. oe 
My reafon for chufing aine drawn through both the {pots . 
rather than through one of ‘them and the center is, firft, that. 
they were not fituated quite oppofite each other, and therefore, | 
unlefs other obfervations: had pointed out which was moft . 
polar, I fhould evidently run the greater rifk in fixing on- 
one of them in preference tothe other. Inthe next place, we - 
find by the fecond obfervation, page 235. that in two hours and * 
a half both {pots were intirely-gone oyt of the difk. This; 
Els 4: plainly 
