Answer: In the given excerpt from Herman Melville’s "The Lightning-Rod Man" we can see a comparison of a salesman with the devil, this similarity is demonstrated in three occasions on the text:
"The scowl grew blacker on his face; the indigo-circles enlarged round his eyes as the storm-rings round the midnight moon. He sprang upon me; his tri-forked thing at my heart", here, the author describes some kind of scary creature with a "tri-forked thing" just like the devil.
"I seized it; I snapped it; I dashed it; I trod it; and dragging the dark lightning-king out of my door, flung his elbowed, copper scepter after him" in this phrase the author calls the salesman "the dark lightning-king"
"But spite of my treatment, and spite of my dissuasive talk of him to my neighbors, the Lightning-rod man still dwells in the land; still travels in storm-time, and drives a brave trade with the fears of man" here the author refers to the salesman as "the Lightning-rod man" also comparing him with the devil.