Mirth is short and transient, cheerfulness fixed and permanent† Mirth is like a flash of lightning that breaks through a gloom of clouds, and glitters for a moment: cheerfulness keeps up a kind of day-light in the mind, and fills it with a steady and perpetual serenity.

-Addison,Joseph
  In The Spectator, no.381,17 May.

Come, my Celia, let us prove, While we can, the sports of love, Time will not be ours for ever, He, at length, our good will sever; Spend not then his gifts in vain: Suns that set may rise again; But if once we lose this light, 'Tis with us perpetual night. Why should we defer our joys? Fame and rumour are but toys.

-Jonson, Ben
  Volpone,'Song', act 3, sc.7.

We have no eternal allies, and we have no perpetual enemies.Our interests are eternal, and it is our duty to follow them.

-Palmerston, HenryJohnTemple, 3rd Viscount
  Speech, House of Commons,1 Mar.

The perpetual hunger to be beautifuland thatthirsttobe loved which is the real curse of Eve.

-Rhys,Jean pseudonym of  Ellen Gwendolen Rees Williams
  The Left Bank,'Illusion'.

A perpetual holiday is a good working definition of hell.

-Shaw, George Bernard
  Parents and Children.

The light in the window seemed perpetual Where you stayed in the high room for me

-Spender, Sir Stephen Harold
  'The Room AboveThe Square'.