On the other hand, the eye-glass must not be of such small focal length that the image appears indistinct and contorted, or dull for want of light.
[Illustration: _Fig.

2._] Let us compare with the arrangement exhibited in fig.

1 that adopted by Galileo.

Surprise is sometimes expressed that this instrument, which in the hands of the great Florentine astronomer effected so much, should now be known as the _non-astronomical Telescope_.

I think this will be readily understood when we compare the two arrangements.
In the Galilean Telescope a small concave eye-glass, _ab_ (fig.