Memory is something that we humans experience in our brains. It basically allows us to store and eventually recall that particular information of those past experiences. If at all we did some thing wrong in the past, our memory would help us in rectifying that mistake by enhancing it.
In relation to the paragraph from the book Invisible Cities, I think memory is referred to – as “relation between the measurements of its space and events of it’s past”. The writer portrays his memory of Zaira as, “the height of a lamppost and the distance from the ground of a hanged usurper’s swaying feet; the line strung from the lamp post to the railing opposite and the festoons that decorate the course of the queen’s nuptial procession; the height of that railing and the leap of the adulterer who climbed over it at dawn; the tilt of a guttering and a eat’s progress along it as he slips into the same window; the firing range of a gunboat which has suddenly appeared beyond the cape and the bomb that destroys the guttering; the rips in the fish net and the three old men seated on the dock mending nets and telling each other for the hundredth time the Story of the gun- 10 boat of the usurper, who some say was the queen’s illegitimate son, abandoned in his swaddling clothes there on the dock.”
In a supernatural world I would be able to relate to such a memory. Like the memory of when a cat progresses along as he slips away into a window. I guess that thought/memory makes me think of an instance where a particular person is deep into remembering a memory but then gets distracted and that particular memory just goes away in a split second and he forgets that that situation ever occurred.
Thus memory can be helpful in many ways and at the same time deadly too.