The advance in technology that made the discovery of cells possible was the invention of the microscope.

Here's why:

* Cells are microscopic: Cells are incredibly small, far too tiny to be seen with the naked eye.

* Microscopes provide magnification: Microscopes allow us to magnify objects, making them appear larger and visible.

While Robert Hooke, credited with the discovery of cells, used a crude compound microscope, it was the key tool that allowed him to see the tiny compartments within a thin slice of cork, which he then named "cells."

Without the development of the microscope, the discovery of cells would have been impossible.