What is the test for determining whether a plaintiff’s suicide was accidental or suicide?

In Harvey v. Ocean Accident and Guarantee Corporation, [1905] 2 I.R. 1, which, however, went off on another point, Lord Justice FitzGibbon states the question of law more fully at p. 29:— “If a man is found drowned, and certainly drowned either by accident or by suicide, and there is no preponderance of evidence as to which of the two caused his death, is there any presumption against suicide which will justify a jury or an arbitrator in finding that the death was accidental and innocent, and not suicidal and criminal? In my opinion there clearly is such a presumption.”