on the Rotation of the Planets , &c. i^y 
I have ventured to calculate the times for that oppofition, 
'■when the edge of the remarkable dark fpot will be feen 
near the center, as it is in figure 23, or, which is the fame 
thing, as it was the nth of May 1 779, at i2h. \ f. The 
fpot not being vifible at the time of the oppofition, I have taken 
the neareft period, before and after, in which it will pafs over 
the difk. There is, 'however, a circumfiance w 7 hich may make 
the appearance of the fpot not quite limilar to the figure I have 
drawn, even though the rotations fliould perfedlly anfwer as to 
the times ; for the poiition of the axis of Mars being ftill in 
fome meafure unknown, I could make no allowance for a 
change, which a difference in the fituation of no lefs than two 
figns may occafion, though in all probability it will not be 
very confiderable. 
Thofe wiio are provided with proper telefcopes will have an 
Opportunity to fee how far the calculated times agree with the 
" pot’s appearance ; and it is by this means I alfo hope to corredt 
and improve the tables I have drawn up for this purpofe, and 
f offer to approximate to a true theory of the gyration of this 
pi net; ' - 
icy. knowing the exacf difference of meridians between 
Greenwich and this place, 1 have calculated the fpot’s ap- 
pearance for the meridian of Bath. From an eclipfe or 
two of Jupiter’s fatellites, of which, by the favour of the Rev. 
Mr. hornsby, I have feen correfpondent obfervations, I fup- 
pofe the difference cannot be much lefs than 9' w T eft of Green- 
wich ; and at the fame time I join an account of the folar 
eclipfe of the 24th of June 1778, which may be depended 
upon as a very compleat obfervation, and may ferve to afcer- 
tain the longitude of this place. 
Vol. LXXI. 
T 
Eclipfe 
