Complex sentence: In many cases the medium in which the wave is being propogated does not permit a direct visual image of the form and an instrument called an oscilloscope is used to pictorially repesent the wave as a repeating image on a crt screen.
Split into simpler sentences: In many cases the medium in which the wave is being propogated does not permit a direct visual image of the form. An instrument called an oscilloscope is used to pictorially repesent the wave as a repeating image on a CRT screen.