Popular imagination presupposes spiritual beings to be utterly independent of gravitation, while retaining shapes and proportions which gravitation originally determined, and only gravitation seems likely to maintain.
When and if spiritual beings make themselves visible either to our bodily eyes or to our inward vision, their object would be thwarted were they not to appear in a recognizable form; so that their appearance would take the shape of the body and clothing to which we have been accustomed.