Let us follow Nietzsche’s lead and try to find the source of the world. Perhaps then we will understand that "unknown country" of which Emerson speaks.
We know that the visible world cannot be the product of the senses, for the senses cannot be a product of themselves. Does it lie in the objects themselves? Is the world “objective,” composed of objects? When we follow any quality of an object to its source we come back to ourselves. What we see as color, as form, as location, can all be traced to our senses and mind. Color blindness is a simple example of this. Those with the most common form of red–green color blindness (deuteranomaly) see less green than a “normally sighted” person. Relative to “normal” their sight is green weak. For them, a full pallet of colors consists of red and blue. Since full pallet mixtures are seen as white (red, green and blue mixtures are seen as white by people with “normal” color vision), deuteranope’s see mixtures of red and blue (i.e., purple) as “white.” About 5% of men and 0.35% of women have this type of color blindness. Because the majority of people see full greens as well as reds and blues, we consider this condition normal and attribute to the object the possession of the full color spectrum seen by those with "normal" color vision. In truth, the qualities possessed by the object are just as much a creation of our senses (and mind) as of the object itself. If we were all deuteranopes, there would be no purple.
The phenomenon of synesthesia demonstrates this even more clearly. Those with synesthesia experience a joining of the senses so that the synesthete may hear colors, or taste shapes. To a synesthete the world is a rich and rewarding place, full of wonder[1]. Melodies have shapes and numbers have color. The existence of synesthesia reinforces the fact that the qualities of objects do not reside in the objects themselves. The same object seen by different observers has different qualities. This fact even extends to the perception of shape and extension[2], qualities which Locke took to be the primary, measurable, objective aspects of external reality. These considerations show us that we cannot find the world in the objects that we perceive. Does it then lie in the atoms?
The world does not lie in the atoms. The atom is a conceptual model used to summarize a great number of experiments and experiences, obtained both through the senses and with the aid of instruments[3]. If we endow the atom with sensory qualities, it is because we learned to visualize it from diagrams intended to simplify the underlying experiments and mathematical formulations. Although we often project the qualities we assign to atoms into the external world, it is important to realize that these qualities are not found there. A model cannot be the basis for the world that we are seeking.
We have sought the basis of the world, and found nothing. The source of our mental power must be found within that power itself, not in an “external world.” Our thought is the harbinger of what flows from that unknown country of which Emerson speaks.
[1] “The perceptual richness of words is for me not just pedantry. Each is unique, and saliently so. They all have different shapes and colors. And even though each letter of a word is colored differently, a word's color isn't simply made up of the colors of its component letters. The shades combine, bleed into each other, change slightly depending on their neighbors.”—Karen Chenausky
[2] Marius von Senden, Space and sight: The perception of space and shape in the congenitally blind before and after operation (Glencoe, IL: Free Press, 1960)
[3] Encyclopædia Britannica, Chemical bonding. Encyclopedia Britannica Online.