For example, consider an electron. There is a scalar distribution of electricity, which is what is ordinarily called the electron. This scalar distribution has a volume-density ρ at the time _t_ at any point (_x_, _y_, _z_). Thus ρ is a function of (_x_, _y_, _z_, _t_), which is zero except within a restricted region. Furthermore, at any time _t_, as an essential adjunct, there is a continuous space distribution at each point of the two vectors (_X_, _Y_, _Z_), which is the electric force, and (α, β, γ), which is the magnetic force. Lastly, individuality is ascribed to the scalar electric distribution, so that in addition to its conservation of quantity--involved in the assumed laws--it is also possible to assign the velocities with which the various individual parts of the distribution are moving. Let (_u_, _v_, _w_) be this velocity at (_x_, _y_, _z_, _t_). This whole scheme of scalar and vector quantities, namely, ρ, (_X_, _Y_, _Z_), (α, β, γ), (_u_, _v_, _w_) is interconnected by the electromagnetic laws. It follows from these laws that the electron, in the sense of the scalar distribution ρ, is to be conceived as at each instant propagating from itself an emanation which travels outwards with the velocity of light _in vacuo_, and from which (_X_, _Y_, _Z_) and (α, β, γ) can be calculated, so far as they are due to that electron. Thus the field, at any time, due to the electron as a whole depends on the previous history of the electron, the nearer to the electron the more recent being the relevant history. The whole scheme of such a field is one single thought-object of science: the electron and its emanations form one essential whole, namely one thought-object of science, essentially complex and essentially filling all space. The electron proper, namely, the scalar distribution ρ, is the focus of the whole, the essential focal property being that the field at any instant is completely determined by the previous history of the focus and of its space relations through all previous time. But the field and the focus are not independent concepts, they are essentially correlated in one organised unity, namely, they are essentially correlated terms in the field of one relation in virtue of which the entities enter into our thoughts. The fields of a group of electrons are superposed according to the linear law for aggregation, namely, pure addition for analogous scalar quantities and the parallelogram law for analogous vectors. The changes in motion of each electron depend entirely on the resultant field in the region it occupies. Thus a field can be viewed as a possibility of action, but a possibility which represents an actuality.