be conscious of

References in classic literature ?
You may be conscious of a friend either by seeing him or by "thinking" of him; and by "thought" you can be conscious of objects which cannot be seen, such as the human race, or physiology.
Unless we are to acquiesce in the view that we can never be conscious of anything outside our own minds, we must say that the object of consciousness need not be mental, though the consciousness must be.
Looking fixedly eastward he seemed to be conscious of some faint lightening in the sky.