Question

Why does John want the ghost to disappear before his wife appeared on the scene?What impression of his wifes character do you form his words?

Answer 1

John wanted Helen (the ghost) to disappear at once because he did not want Lavinia to see Helen, the ghost. She was a very sensitive woman and subject to hysterics. She usually could not stand the sight of a mouse, just imagine what the sight of a ghost in the living room would do to her!

This shows Lavinia was quite a timid in handling ghosts and mice. 

Answer 2

Thank you for asking this question.
 let me help you in finding the answer.
Actually john does not want to Helen(who is a ghost) to be seen by his wife  because he know his wife's nature .That she is too sensitive and is even scared of a mice if she see the ghost named as Helen she will definitely gets terrifies of it . This is the reason John was to Helen to disappear before his wife.