458 Dr. Herschei/s Observations and Remarks on the 
200 or 160, with which I have seen the figure of Saturn, is 
not sufficient to show it to one who has not already seen it 
perfectly well with an adequate high power ; an observer, 
therefore, who has not an instrument that will bear a very 
distinct magnifying power of 500, ought not to expect to see 
the outlines of Saturn so sharp and well defined as to have a 
right conception of its figure. The quintuple belt is generally 
a very good criterion ; for if that cannot be seen the telescope 
is not sufficient for the purpose ; but when we have intirely 
convinced ourselves of the reality of the phenomena I have 
pointed out, we may then gradually lower the power, in 
order to be assured that the great curvature of the eye- 
glasses giving these high powers, has not occasioned any 
deceptions in the figure to be investigated, and this was the 
only reason why I mentioned that I had also seen the re- 
markable figure of Saturn with low powers. 
In very critical cases it becomes necessary to calculate 
every cause of an appearance that falls under the province of 
mathematical investigation. For this reason I have always 
looked upon an astronomical observation without a date as 
imperfect, and the journal-method of communicating them is 
undoubtedly what ought to be used. For instance, when it 
is known that my last year’s most decisive observation, 
relating to the singular figure of Saturn, was made the 5th of 
May, astronomers may then calculate by this date the place 
of Saturn and of the earth ; their distances from each other, 
and the angle of illumination of the Saturnian disk ; by these 
means we find the gibbosity of the planet in the given situa- 
tion, and ascertain that the defalcation of light could not 
then amount to the one hundredth part of a second of a 
