This section is from the book "Popular Law Library Vol7 Equity Jurisprudence, Trusts, Equity Pleading", by Albert H. Putney. Also available from Amazon: Popular Law-Dictionary.
Two great distinctions are to be noticed between accident and mistake. In the first place mistake is subjective, while accident is objective. Mistake is in the minds of the parties, while accident is external thereto. Secondly, mistakes take place at the time the contract is entered into, while accident happens after the contract has been made or the right acquired which suffers injury by the accident.