Microscope, Telescope, Interferometer 37 ence in the path of the two pencils is not too great, and provided that the two pencils are reunited at a sufficiently small angle. By altering these conditions of reflection or | 38 Light Waves and Theib Uses refraction we may obtain a very considerable number of variations of form, as illustrated in Figs. 34, 35. One of these types, enlarged in Fig. 36, has been arranged |