How does Harper Lee create atmosphere during the trial scenes of the novel To Kill a Mockingbird?

In Chapter 17 with detailed and vivid description, Harper
Lee creates a tableaux of the momentous event that the trial of Tom Robinson becomes for
the residents of Maycomb County; Scout describes the occasion as "like
Saturday":

People from the south end of the county passed
our house in a leisurely but steady stream.

Mr. Dolphus
Raymond lurched by one his thoroughbred.... A bearded man in a wool hat drove them.
"Yonder's some Mennonites,"...A wagon load of unusually stern-face citizens appeared.
When they pointed to Miss Maudie Atkinson's yard, Miss Maudie herself came out on the
porch...standing with arms akimbo,...We knew she wore a grin of uttermost
wickedness.

When the driver quotes scripture, Miss Maudie
returns with scripture; Scout remarks that they must have thought she quoted the Devil
as they sped up.

With this description, Lee paints
hypocrisy into her tableau as a strict religious sect that shuns the way of the world by
not wearing buttons and by living a simplified life who, nevertheless, feel such worldly
curiosity that they come to attend Robinson's trial. Of course, the Fundamentalists who
heckle Miss Maudie epitomize this hypocrisy. And with a bold brush stroke of the
underlying hypocrisy of the town, Mr. Dolphus Raymond lurches past on his fine
horse.

Another phrase that suggests the spectacle of human
curiosity for the misfortune of others and the circus that the trial is to become is
Scout's "It was a gala occasion." The courthouse square is filled with people who set up
a picnic: "Some people were gnawing on cold chicken and cold fried pork chops." Scout's
use of the word gnawing is significant as there is the sense of a
predatory animal. And, with the "Negroes [who] sat quietly in the sun and Mr. Raymond
drinks from a bag with two yellow straws" the evil to be committed against Tom by the
whites, is subtly foreshadowed by Lee's use of yellow, a color so often symbolic of
evil.

Then, too, the reader cannot but notice the symbolism
of this description of the courthouse:

But for the
southporch, the Maycomb County courthouse was early
Victorian,presenting an unoffensive vista when seen from the
north. From the other side, however, Greek revival columns
clashed with a big nineteenth-century clock tower housing a
rusty unreliable instrument, a view indicating a people determined to
preserve every physical scrap of the
past.

Similarly, the old men of the Idlers'
Club are "resentful of the interruption of their comfortable routine" hint at the
community's desire to preserve the status quo, "Atticus aims to defend him. That's what
I don't like about it." In addition, the turmoil and defeat to come inthe trial is
suggested with Scout's recounting of the one time that Judge Taylor was "ever seen at a
dead standstill in open court, and the Cunninghams stopped
him."

In the trial scenes, Bob Ewell mirrors the Idlers'
Club with his attitude. His moral and intellectual degeneracy is displayed in his speech
as he describes Mayella "like a stuck hog inside the house--" and his reference to Tom
as "that black n--- yonder ruttin' [like an animal] on my Mayella!" His eying of Atticus
with suspicion also suggests the turmoil to come. Likewise, Mayella's display of
ignorance and circumventions casta pall upon Tom's chances for justice as the trial is
interrupted by frivolousness when she accuses Atticus of "sassing her." Then, Mr.
Gilmer's prosecuting "almost reluctantly" furthers the dismal prospects for
Tom.