on the Rotation of the Planets, Sic. 137 
I have ventured to calculate the times for that opposition, 
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 1779? at 12I1. if. The 
fpot not being vifible at the time of the oppofition, I have taken 
the neared: period, before and after, in which it will pafs over 
the difk. There is, however, a circumftance which may make 
the appearance of the fpot not quite Similar to the figure I have 
drawn, even though the rotations Should perfectly anfwer as to 
the times ; for the politic 11 of the axis of Mars being Still in 
fome meafure unknown, I could make no allowance for a 
change, which a difference in the Situation of no lefs than two 
Signs may occasion, though in all probability it will not be 
very considerable. 
ThoSe who are provided with proper telefcopes will have an 
opportunity to fee how far the calculated times agree with the 
fpot’s appearance ; and it is by this means I alfo hope to cor reft 
and improve the tables I have drawn up for this purpofe, and 
further to approximate to a true theory of the gyration of this 
planet. 
Not knowing the exa <£t difference of meridians between 
Greenwich and this place, I have calculated the fpot’s ap- 
pearance for the meridian of Bath. From an eclipfe or 
two of Jupiter’s Satellites, of which, by the favour of the Rev. 
Mr. hornsby, 1 have feen correspondent observations, I fup- 
pofe the difference cannot be much Ids than f weft 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 observation, and may Serve to afeer- 
tain the longitude of this place. 
Vol. LXXI. 
T 
Eclipfe 
