2), is placed between the object-glass and the image.

In fact, no image is allowed to be formed in this arrangement, but the convergent pencils are intercepted by the concave eye-glass, and converted into parallel emergent pencils.

Now in fig.

2 the concave eye-glass is so placed as to receive only a part of the convergent pencil A _p_ B, and this is the arrangement usually adopted.

By using a concave glass of shorter focus, which would therefore be placed nearer to _m p_, the whole of the convergent pencil might be received in this as in the former case.