When he got the mystery in focus he suddenly stopped and rubbed the object-glass with his handkerchief.
In the Galilean Telescope a small concave eye-glass, ab (fig. 2), is placed between the object-glass and the image.
He had an object-glass of 15 feet (French) focus, and this he mounted in a tube formed of “four pine planks.”
Following these indications, it will be found easy to direct the tube, so that the object-glass shall appear full of light.
It contains a telescope made by Fitz, whose focal length is seventeen feet, and its object-glass is twelve and a half inches.
