We are instinctively willing to believe that by due attention, more can be found in nature than that which is observed at first sight.

But we will not be content with less.
What we ask from the philosophy of science is some account of the coherence of things perceptively known.
This means a refusal to countenance any theory of psychic additions to the object known in perception.

For example, what is given in perception is the green grass.

This is an object which we know as an ingredient in nature.

The theory of psychic additions would treat the greenness as a psychic addition furnished by the perceiving mind, and would leave to nature merely the molecules and the radiant energy which influence the mind towards that perception.