The focusing should therefore next be attended to, the increase of clearness in the image being the test of approach to the true focus.

And again, it will be well to try the effect of slight changes of distance between the screen and the telescope's eye-piece.

Mr.Howlett considers one yard as a convenient distance for producing an excellent effect with almost any eye-piece that the state of the atmosphere will admit of.

Of course, the image becomes more sharply defined if we bring the screen nearer to the telescope, while all the details are enlarged when we move the screen away.

The enlargement has no limits save those depending on the amount of light in the image.