what he does not know. The distinctness of the errors is a merit; it
proceeds from the clear-headedness of the author. The suppression in the
journals may be due partly to admiration of the talent and energy which
lived two difficult lives at once, partly to respect for high position in
public affairs, partly to some of the critics being themselves men of
learning only, unable to detect the errors. But we know that action and
reaction are equal and contrary. If our generation take no notice of
defects, and allow them to go down undetected among merits, the next
generation will discover them, will perhaps believe us incapable of
detecting them, at least will pronounce our judgment good for nothing, and
will form an {164} opinion in which the merits will be underrated: so it
has been, is, and will be. The best thing that can be done for the memory
of the author is to remove the unsound part that the remainder may thrive.
The errors do not affect the work; they occur in passages which might very
well have been omitted: and I consider that, in making them conspicuous, I
am but cutting away a deleterious fungus from a noble tree.

(P. 154). The periodic times of the five planets were stated by
Eudoxus,[286] as we learn from Simplicius;[287] the following is his
statement, to which the true times are subjoined, for the sake of
comparison:

STATEMENT OF EUDOXUS TRUE TIME
Mercury 1 year -- 87d. 23h.
Venus 1 " -- 224d. 16h.
Mars 2 " 1y. 321d. 23h.
Jupiter 12 " 11y. 315d. 14h.
Saturn 30 " 29y. 174d. 1h.

Upon this determination two remarks may be made. First, the error with
respect to Mercury and Venus is considerable; with respect to Mercury, it
is, in round numbers, 365 instead of 88 days, more than four times too
much. Aristotle remarks that Eudoxus distinguishes Mercury and Venus from
the other three planets by giving them one sphere each, with the poles in
common. The proximity of Mercury to the sun would render its course
difficult to observe and to measure, but the cause of the large error with
respect to Venus (130 days) is not apparent.

{165}

Sir G. Lewis takes Eudoxus as making the planets move round the sun; he has
accordingly compared the _geocentric_ periods of Eudoxus with our
_heliocentric_ periods. What greater blunder can be made by a writer on
ancien