The periodicaltimes of all the satellites. --Sir J.
Herschel.
2. Performed in a period, or regular revolution; proceeding
in a series of successive circuits; as, the periodical
motion of the planets round the sun.
3. Happening, by revolution, at a stated time; returning
regularly, after a certain period of time; acting,
happening, or appearing, at fixed intervals; recurring;
as, periodical epidemics.
The periodic return of a plant's flowering.
--Henslow.
To influence opinion through the periodical press.
--Courthope.
4. (Rhet.) Of or pertaining to a period; constituting a
complete sentence.
{Periodic comet} (Astron.), a comet that moves about the sun
in an elliptic orbit; a comet that has been seen at two of
its approaches to the sun.
{Periodic function} (Math.), a function whose values recur at
fixed intervals as the variable uniformly increases. The
trigonomertic functions, as sin x, tan x, etc., are
periodic functions. Exponential functions are also
periodic, having an imaginary period, and the elliptic
functions have not only a real but an imaginary period,
and are hence called doubly periodic.
{Periodic law} (Chem.), the generalization that the
properties of the chemical elements are periodic functions
of their atomic wieghts. ``In other words, if the elements
are grouped in the order of their atomic weights, it will
be found that nearly the same properties recur
periodically throughout the entire series.'' The following
tabular arrangement of the atomic weights shows the
regular recurrence of groups (under I., II., III., IV.,
etc.), each consisting of members of the same natural
family. The gaps in the table indicate the probable
existence of unknown elements.