Walden incorporates visual imagery in order to convey an essential tenet of Transcendentalism: standing in awe of nature's beauty. In "Baker Farm" the author writes:
Once it chanced that I stood in the very abutment of a rainbow’s arch, which filled the lower stratum of the atmosphere, tinging the grass and leaves around, and dazzling me as if I looked through colored crystal. It was a lake of rainbow light, in which, for a short while, I lived like a dolphin. If it had lasted longer it might have tinged my employments and life. As I walked on the railroad causeway, I used to wonder at the halo of light around my shadow, and would fain fancy myself one of the elect. One who visited me declared that the shadows of some Irishmen before him had no halo about them, that it was only natives that were so distinguished.
Examples of imagery include the rainbow's location and how close it is to the Earth in "the lower stratum of the atmosphere." Thoreau also compares the rainbow's abutment to a "lake of rainbow light" in which he reveled. The "halo of light around [his] shadow" and the "tinging," "dazzling," "colored crystal" of the rainbow comprise powerful images of light and color. If one takes a step back to consider this scene, it seems impossible that the rainbow should abut the railroad, because the serendipitous convergence of these symbols seems almost too good to be true. However, the detailed imagery makes it seem very real.
Whether or not Thoreau embellished this moment, it illustrates the sheer beauty of nature and the importance of taking the time to appreciate its presence. Experiences like this help people transcend themselves and go beyond the daily drudgeries in order to experience a higher form of consciousness—hence the name of the "Transcendentalist" movement, of which Thoreau was an essential part. In this passage and many others, Thoreau includes detailed imagery to permit the reader to live vicariously through him during these ecstatic moments, with the final goal of convincing people to reconvene with nature.
In "Brute Neighbors" Thoreau employs personification and dramatic visual imagery to describe a "war" between two groups of ants:
One day when I went out to my wood-pile [...] I observed two large ants, the one red, the other much larger, nearly half an inch long, and black, fiercely contending with one another. Having once got hold they never let go, but struggled and wrestled and rolled on the chips incessantly [...] the chips were covered with such combatants, that it was not a duellum, but a bellum, a war between two races of ants, the red always pitted against the black, and frequently two red ones to one black. The legions of these Myrmidons covered all the hills and vales in my wood-yard, and the ground was already strewn with the dead and dying, both red and black.
Here, Thoreau discovers two ants fighting with each other. Visual imagery helps convey that they are not the only combatants; the fight is not a duel but a war: "the chips were covered" in ants. He also specifies the large size of the black ant as being "nearly half an inch long." Color imagery includes the phrase "the red always pitted against the black."
The drama in this passage comes mainly from the war language (which could be categorized as personification). And an allusion to an ancient Greek battle conveys the extent of the damage and death among the ants as "legions of these Myrmidons covered all the hills and vales." This example of personification makes this passage relevant to the rest of Walden because it dramatizes a small struggle among animals and subtly reflects challenging relationships among humans. Here and elsewhere, Thoreau takes inspiration from nature and draws comparisons between the animal and human worlds. It is very important to note that his comparison is sincere. He does not use any sarcasm when he likens ants to heroes in ancient legends. He rather wants to remind the reader that while not everything in nature is as peaceful as the placid Walden Pond, most creatures have a certain grace or beauty that recalls the virtues of humanity.