“The sun had sunk low in the west and, behind London’s dome of smoke, shone the color of a horseshoe when the farrier beats it out on the anvil.” (Stephenson 2004, 274)
This passage is a great demonstration about metaphors and an issue I have with them. There are two useful deployments of the metaphor. First, the metaphor helps describe something. The second use is to further the scene, not in description but in quality.
The above metaphor helps describe the London sky and also helps establish the time period by other reference to industry that would normally be found in London at that time. But few of us know about the image of horseshoe being beaten on an anvil. It is a technology of the time of the story and helps convey a sense of the setting, but it does miss something in the mediation between Stephenson and the reader. A metaphor which spoke to the contemporary condition, one we as the reader are familiar with would succeed in being more descriptive. But that alternative would then lose the sense of the setting Stephenson is working at. What we have here then is that the two deployments of the metaphor are at odds with each other. It is one of the paradoxes of language, not at all unlike supply and demand curves.
Stephenson, Neal. (2004). The System of the World. NY: Harper Perennial.