According to the popular New Zealand entertainer, broadcaster and etymological author Max Cryer MBE (2010) Lady Sydney Morgan coined the oxymoronic phrase 'accidentally on purpose' in 1862. He is wrong – as Big Data research has proved already so many of his other published 'originator' claims to be – and will, no doubt, demolish many others before it is done!
In my own research, using the ID research method in Google's Library project, I found that Sydney, Lady Morgan was apparently first to coin a phrase later used by Charles Darwin – namely, 'nature’s own selection' (see Sutton 2014 for details of who else used it in a socio-biological survival of the fittest sense before Darwin (1859) used it in the Origin of Species.
Big Data Strikes Again! The phrase 'accidentally on purpose' was in fact published at least as early as 1727 by the historian John Odmixon and occurs in over 100 different books between 1727 and Cryer's fallacious claimed first coinage of the phrase in 1862.
John Odmixon (1727)Clarendon and Whitlock Compar'd: To which is Occasionally Added, A Comparison Between the History of the Rebellion, and Other Histories of the Civil War. : Proving Very Plainly, that the Editors of the Lord Clarendon's History, Have Hardly Left One Fact, Or One Character on the Parliament Side, Fairly Represented . p. 93. Fleet Street. J. Pemberton.
NOTE (The OED gets back even further to 1711 (darn it to hell!)
So, Dear Reader, please don't be convinced too easily by any so-called 'expert' histiographer, etymologist or other fogey seeking to convince you that searching Google Books is second-rate compared with traditional “expert” archive research. Because the ID method cuts through such claptrap like a buzz-saw in “bulloney”!
Cryer, M. (2010) Who Said That First? Auckland New Zealand. Exisle Publishing Ltd.
Sutton, M. (2014) Nullius in Verba: Darwin's Greatest Secret. USA. ThinkerMedia. Inc.