Mr. G. Goodwill, in opening this discussion, said that in dealing with the subject of units in mechanics, it seemed to him to be a help, in the first place, to recognize that, in general, when expressing the value of any quantity, the unit employed belonged to one of two kinds, determined by the business in hand. It would be either (a) a unit represented simply by a well-recognised amount of the quantity itself, or (b) a unit which, in the simplest possible way, took account of the relations of the quantity with others with which they might at the same time be concerned.