Where the will shows an intention that the second bequest shall take effect only in the event of the first bequest failing in a particular manner, the second bequest shall not take effect, unless the prior bequest fails in that particular manner.
     Illustration
     A makes a bequest to his wife, but in case she should die in his lifetime, bequeaths to B that which he had bequeathed to her. A and his wife perish together, under circumstances which make it impossible to prove that she died before him, the bequest to B does not take effect.