In this important contribution to theoretical physics, Donald Rait McGregor presents a major "The vacuum has a demonstrable inertial characteristic of such a nature and of such a wide relationship to physical phenomena and experiments that it should be considered as the basis for a new, more comprehensive understanding of physical actions." McGregor notes that the inertia of the vacuum can be used as the basis for a new physics theory structure. As he explains, however, "this does not mean that our inherited concepts of time and space must be abandoned. It means that a very useful new partner has been suggested to join them." McGregor first asks how large a volume of space must be to have the fundamental characteristics of the vacuum. He finds the answer by examining the internal structure of the atom, then proceeds to calculate the inertia of the vacuum by analyzing two well-known experiments from a new perspective. According to McGregor, "The new idea that the vacuum has inertia as an inherent characteristic provides basic physics theory with a new opportunity to develop and test a more comprehensive theory structure, which may turn out to be more closely in accordance with more actual physical experiments than some of our inherited physics theories."