( We ( ( ( ( distinguish here ) ( between ( mechanical waves ) ) ) ( where ( there ( is ( ( ( ( ( a ( tangible medium ) ) ( ( in which ) ( ( the wave ) travels ) ) ) , ) and ) ( ( other types ) ( of ( waves ( where ( ( the medium ) ( ( is not ) ( so evident ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBD distinguish) (ADVP (RB here)) (PP (IN between) (NP (JJ mechanical) (NNS waves))) (SBAR (WHADVP (WRB where)) (S (NP (EX there)) (VP (VBZ is) (NP (NP (NP (DT a) (JJ tangible) (NN medium)) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (DT the) (NN wave)) (VP (VBZ travels))))) (, ,) (CC and) (NP (NP (JJ other) (NNS types)) (PP (IN of) (NP (NP (NNS waves)) (SBAR (WHADVP (WRB where)) (S (NP (DT the) (NN medium)) (VP (VBZ is) (RB not) (ADJP (RB so) (JJ evident))))))))))))) (. .)))
We distinguish here between mechanical waves where there is a tangible medium in which the wave travels, and other types of waves where the medium is not so evident.
(ROOT (S (NP (NP (NNP Matter)) (SBAR (IN that) (S (NP (JJ mechanical) (NN wave) (NN energy)) (VP (MD can) (ADVP (RB only)) (VP (VB travel) (PRT (RP through))))))) (VP (VBZ is) (ADJP (JJ medium))) (. .)))
Matter that mechanical wave energy can only travel through is medium.