Hearing - one of our five senses.
Effect here means, of course, musical effect in the ear's appreciation of the notes. [Scientific Basis and Build of Music, page 28]
Probably the lowest harmony which we have the power of partially hearing is A minor, rising in the lower series of seven octaves; C, its highest note, sounding the six tones of C, its major harmony, on our horizon of sound. The diagram begins with A, the second space of the treble clef, as most convenient for writing. [Harmonies of Tones and Colours, The Minor Harmonies, page 33a]
Christ Returns - Speaks His Truth
"I was shown the following vivid vision.
First of all, I saw a new-born babe as 'light', a life-form of 'Creative Power'.
As the baby grew into childhood, then manhood, I saw the pure LIGHT of the 'Creative Power' gradually dimmed and then obscured altogether in him, by a dense wrapping of chains and thongs.
I questioned the meaning of the vision and there came to my mind a clear understanding which may be expressed in the following words:
'From birth to death - people believe and insist that their five senses of sight, hearing, touch, smell and taste, correctly predicate the 'reality' of themselves and the universe around them.
Therefore, because they draw their mind power direct from Divine 'Creative Power', it is done to them according to their beliefs. [Christ Returns - Speaks His Truth, Letter 1, page 17]
"The human ear, like those of other mammals, is so extraordinarily sensitive that it can detect sound-wave-induced vibrations of the eardrum that move by less than the width of an atom. Now, researchers at MIT have discovered important new details of how the ear achieves this amazing ability to pick up faint sounds." Read more at: https://phys.org/news/2019-01-mechanism-ear-exquisite-sensitivity.html#jCp