premise: It had been found in Mrs. Inglethorp's cheque book, and on being reversed at a mirror, showed clearly the words: " ¦ erything of which I die possessed I leave to my beloved husband Alfred Ing  ¦ " This placed beyond question the fact that the destroyed will had been in favour of the deceased lady's husband. 
hypothesis: Mrs.Inglethorp knew that it was in her cheque book. 