How is Helen able to enjoy Niagara Falls without hearing or seeing it?

From the text:

We went to Niagara in March, 1893. It is difficult to describe my emotions when I stood on the point which overhangs the American Falls and felt the air vibrate and the earth tremble.

It seems strange to many people that I should be impressed by the wonders and beauties of Niagara. They are always asking: "What does this beauty or that music mean to you? You cannot see the waves rolling up the beach or hear their roar.