Happiness meter:
If at all there is a machine which can measure happiness then it will be available more with the poor. There is a study which shows people in tirrd world are more happier than their brotheren in the west.

In your own case:
If you are very attentive and allert you yourself can see that your happiness keep coming down as you grow rich[to realise this you should be very attentive ] and you can check the same with people who have grown from rags to riches.