340 Mr. herschel’s AJlronomical Obfervations 
this lhape might arife from that caufe, for other low 
liars were alfo irregular in their forms, yet bellatrix was 
exceedingly fine and quite round. 
Oil. 7, 1779, The periodical liar was perfectly round 
in the telefcopes, and its apparent diameter well defined, 
full, and very large, for a liar of that magnitude. 
When I fpeak of the apparent diameter, I would he 
underflood to diftinguifh it not only from the real dia- 
meter, but alfo (if I may bp allowed the expreffion) from 
the real apparent diameter. To explain this a little more 
at large : the body of the fun, for inftance, is of a certain 
dimenfion which we call his real diameter, and this re- 
mains always the fame. His apparent diameter (which 
I here call real apparent) is changeable, according as we 
approach to, or recede from, him, and is between 3 1/ 33". 
and 32' 39"; but were he removed to the dill an ce of 
one of the neareft fixed liars, neither his real, nor real 
apparent diameter, could then be known to us by any 
method we have hitherto been acquainted with: for at the 
diftance of at leall 20 billions of miles, his real apparent 
diameter could not much exceed thirty fourths of a de- 
gree; and a telefcope mull magnify above fourteen thou- 
fand times to make him appear of only two minutes in 
diameter, which llill is hardly fufficiently large to diftin- 
guifh a fquare from a circle : and yet I doubt not, but 
A that 
Of 
