2. what is the primary imagery in “the snow-storm” by ralph waldo emerson? how does that imagery convey the theme of the poem?

The primary imagery in Emerson's poem is clearly seen in the beginning with these lines: 

Announced by all the trumpets of the sky, Arrives the snow, and, driving o'er the fields, 
Seems nowhere to alight: the whited air 
Hides hills and woods, the river, and the heaven, 
And veils the farm-house at the garden's end. 

The imagery stimulates the senses that the weather is changing and that the looming snow-storm is about to begin. It generally describes how the said weather is about to take place by giving the reader a clear picture how the environment transitions.