We therefore interpose a small convex glass _ab_ (called an eye-glass) between the image and the eye, at such a distance from the image that the divergent pencil of rays is converted into a pencil of parallel or nearly parallel rays.

Call this an emergent pencil.

Then all the emergent pencils now converge to a point on the axial line _m_M (produced beyond _m_), and an eye suitably placed can take in all of them at once.

Thus the whole, or a large part, of the image is seen at once.

But the image is seen inverted as shown.