This page defines a Rail Cipher coding. For this we add a number of "rails", and add the characters in sequence, such as for three rails (taken from Wikipedia):
'WEAREDISCOVEREDFLEEATONCE', gives: W . . . E . . . C . . . R . . . L . . . T . . . E . E . R . D . S . O . E . E . F . E . A . O . C . . . A . . . I . . . V . . . D . . . E . . . N . . to give: WECRL TEERD SOEEF EAOCA IVDEN