Observation: The expression cruelty has not been defined in the Act. Cruelty can be physical or mental. Cruelty which is a ground for dissolution of marriage may be defined as willful and unjustifiable conduct of such character as to cause danger to life, limb or health, bodily or mental, or as to give rise to a reasonable apprehension of such a danger.

Held: To constitute cruelty, the conduct complained of should be "grave and weighty" so as to concluded that the petitioner spouse cannot be reasonably expected to live with the other spouse. It must be something more serious than "ordinary wear and tear of married life.