In her essay, "On the Supernatural in Poetry" (The New Monthly Magazine 7, 1826, pp 145-52), Radcliffe writes that terror is the possibility of the horrible, and that it is characterised by "obscurity" or indeterminacy where horror is the realization of that which is dreaded.
Radcliffe makes the further distinction that terror "expands the soul and awakens the faculties to a high degree of life" as the senses become hyperactive. This is particularly significant because she makes no difference in this capacity of terror in relation to negative and "positive horror" fictions. It is the indeterminacy (terror) in positive horror which makes the experience of the sublime possible, the dreadful awe that is evident in poems such as William Blake's "Tyger."
Negative horror is its realization, and in opposition to the effects of terror, actually experiencing horror "freezes and nearly annihilates" the faculties as the dreaded event paralyzes the mind.