We know no spectacle so ridiculous as the British public in one of its periodical fits of morality.
— Thomas Babington Macaulay

By law of periodical repetition, everything which has happened once must happen again and again -- and not capriciously, but at regular periods, and each thing in its own period, not another's and each obeying its own law.
Mark Twain periodical quote

If we glance at the most important revolutions in history, we see at once that the greatest number of these originated in the periodical revolutions of the human mind.
— Karl Wilhelm Von Humboldt

The power of the periodical press is second only to that of the people.
— Alexis de Tocqueville

If we glance at the most important revolutions in history, we see at once that the greatest number of these originated in the periodical revolutions on the human mind.
— Wilhelm von Humboldt