494 
Mr. herschel’s Account 
TABLE 
x. Meafures of the Comet’s diameter *. 
Days. 
March 17 
*9 
21 
28 
April 
29 
2 
6 
18 
// /// 
2 53 
2 59 
3 33 
4 7 
3 58 
4 7 
4 25 
4 25 
4 53 
5 11 
5 20 
5 2 
Powers. 
932. 460. 
932. 460. 
460. 
93 2 ) thefe meafures agree to 9"'. 
227 J 
227 rather too finall a mealure. 
227 fcems right. 
227 
227 
227 very good ; not liable to half a fecond of error. 
227 true to I'z " or 18 " at molt. 
Having meafured the diameter of the Comet with fuch 
hip-h power as 932 and 460, it may not be amifs to make one 
abfervation on this fubjeft, left it (hould be mifapprehended 
that I pretend to a diftincft power of fuch magmtude upon all 
celeftial objefts in general. By experience I have found, that 
the aberration or indiftinftnefs occaftoned by magnifying much, 
provided the objecft be ftiil left Sufficiently diftinft, is rather to 
be put up with, than the power to be reduced, when the angles 
to be meafured are extremely finalL The reafon of this may, 
perhaps, be that a fmall error of judgement, to which we are 
always liable, is of great confequence with a low power, as 
bearing a confiderable proportion to the diameter of the cojed , 
« There are feveral optical deceptions which may affea the meafures of objects 
that fubtend extremely fmall angles. Thus I have found, by -pe-nce ^ that a 
— ^ f rtrsr ; it 
when we become familiar wuh it. I Hero 
il ,h„ „ b- .. — , rri 
,„™gh underilood to . w l, a 1 !•»= >l«» *“ h ' h '^ hereas 
( 
