Dickens is painting a picture in words. If he began the passage with "As I look, I see..."
...yes, it might make more syntactic sense.
Instead, Dickens not only paints the picture, but in words that swirl without the usual syntactic containment in definite sentences...just like fog swirls all around us, unpalpable, seemingly never ending.
He then grounds the four or so opening paragraphs when he writes:
The raw afternoon is rawest, and the dense fog is densest, and the muddy streets are muddiest near that leaden-headed old obstruction, appropriate ornament for the threshold of a leaden-headed old corporation, Temple Bar. And hard by Temple Bar, in Lincoln’s Inn Hall, at the very heart of the fog, sits the Lord High Chancellor in his High Court of Chancery.
WOW. Now that's a wordsmith!
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