The terrestrial telescope, which must give images right side up with respect to the object, differs from the astronomical telescope only in the eyepiece which, in most cases, is made with an astronomical eyepiece before which is placed an inverting device known as the erecting system.
The one we present is a brass pocket terrestrial telescope with five drawtubes. When closed, it is 10.3 cm long and when extended to the fullest 30 cm. The external diameter is 2.4 cm and it is veneered in mahogany.
The objective has a 13.5 cm focal length and a diameter of 18 mm.
A planoconvex erecting lens with a focal length of 23 mm and a diameter of 11 mm is placed at the end of the next-to-last of the inner drawtubes, with the flat side facing the objective at a distance of 17 cm from the latter. ...continues