of the variable Star ih Sobieski's Shield. 145 
bright parts contrasted by considerable intervals or diminutions 
of light. 
7th, and last. We may obtain some idea of the relative 
situation or intervals between these bright parts, by the observa- 
tions of the increase and decrease of brightness, as thereby the 
changes and times elapsed are pointed out. (See Table V. 
page 136 ; and Phil. Trans, for 1797.) 
I have tried practically the effect of the above suppositions, 
by placing small white spots on a dark sphere, which being 
revolved round represented the various changes as nearly as 
could be expected : proceeding therefore with these and other 
considerations, I shall make ideal drawings of the star with the 
small illuminated parts in its atmosphere, and apply to them 
some of the actual observations from both the preceding Tables, 
having always in view that each period may, more or less, 
require a different disposition of spots, in consequence of their 
constant changeability. 
1st View. 
Plate II. Fig. 1, A B, the star’s polar axis, round which its 
rotation takes place in 6 2 days from C to D. 
CD, its equator, the 360 degrees of which being revolved 
in 62 days, gives nearly 5^ degrees for each day’s motion ; the 
brightest part or spot is represented as centrally facing us, 
arid accordingly shewing the star in its greatest lustre. Were 
this bright spot and the other parts to remain unchangeable 
they would after having completed the revolution of 360 de- 
grees or 62 days, (the star’s rotation on its axis,) appear 
again as at first, and at every return continue to give exact 
periodical times, as was nearly the case in 1799 between August 
and October, (See Table IX. p. 142,) but if the spot becomes 
MDCCCV. U 
