i6 2 Dr. Herschel's Observations of a Comet , 
Many observations were made afterwards, which all con- 
firm the reality of this appearance. 
It is so natural for us to reflect upon the cause of a new 
phenomena, that I cannot forbear giving an opinion on this 
subject. To suppose a real change in the whole zone of the 
planet, cannot be probable ; it seems therefore that this ap- 
pearance must be, as my friend calls it, an illusion. But since 
the reality of this illusion, if I may use the expression, has 
been ascertained by observation, it is certain that there must 
be some extrinsic cause for its appearance ; and also that the 
same cause must not act upon the northern hemisphere. Now 
the only difference in the circumstances under which the two 
polar regions of Saturn were seen in the foregoing observa- 
tions is the situation of its ring, which passes before the planet 
at the south, but behind at the north. The rays of light there- 
fore which come to the eye from the very small remaining 
southern zone of the saturnian globe, pass at no great distance 
by the edge of the ring, while those from the north traverse 
a space clear of every object that might disturb their course. 
If therefore we are in the right to ascribe the observed illu- 
sion to an approximate interposition of the ring, we have, in 
the case under consideration, only two known causes that can 
modify light so as to turn it out of its course, which are in- 
flection and refraction. The insufficiency of the first to ac- 
count for the lifting up of the protuberant small segment of 
the northern regions will not require a proof. The effects of 
refraction on the contrary are known to be very considerable. 
Let us therefore examine a few of the particulars of the case. 
The greatest elevation of the visible segment above the ring 
did not amount to more than one second and three or four 
