“Cruelty cases, more than any other class of case, depend particularly on a careful estimate of the witnesses. For in a cruelty case, the question is whether this conduct by this man to this woman, or vice versa is cruelty. How far a spouse has to depart from the normal standards of kindness and self-control that are the basis of married life and how great an effect that departure has to have on the other spouse before it constitutes cruelty is always a question of degree, depending largely on the temperament, circumstances and health of each party. To attempt to decide that question in such a case as this without seeing the parties or their witnesses would be harzardous business, and an appellate court does not lightly embark on it. Lord Thankerton in the case of Watt (or Thomas) v. Thomas [1947] A.C.484, 487, 488 sums up the effect of the cases on this point, and says that the principles embodied therein may be stated in three propositions which my Lord has just read out.”