The duo appeared to be making for a nearby patch of woods, now and then casting apprehensive looks upward at the enormous gasbag of the descending Inconvenience, quite as if it were some giant eyeball, perhaps that of Society itself, ever scrutinizing from above, in a spirit of constructive censure. -- Against the Day, p. 13
In AtD this happens when the Chums of Chance drop in on the fabled "White City" of the 1893 Columbian Exposition. But I've also had a more recent experience of being observed by an enormous eye above the streets of Chicago. It was 1994, and the Art Institute of Chicago was showing their great "Odilon Redon: Prince of Dreams" exhibit. Redon's truncated head in the sky with its great eye staring down at a sailboat on a calm and placid sea ("Guardian Spirit of the Waters," charcoal, 1878) was reproduced on one of the exhibit banners, as illustrated in the rather dithery drawing I made at the time. It was like a logo, branding Redon (in keeping with the marketing metaphor, the reproduction of the original charcoal drawing was apparently colorized by an art director -- but, hey, if you own it, as the Art Institute does, I guess you can do whatever you want). Though it's out of print, used copies of the authoritative critical study and catalogue are still listed at Amazon, at prices ranging from $225 to $535 for the hardcover.
It was more than one eye -- it was many eyes, since the banners were hung along Michigan Avenue for a mile or so. The effect was haunting. Wherever you went, the all-seeing eye was following you. I wonder if Pynchon attended the exhibit. Wouldn't be surprised.
Chumps of Choice is a group blog by a number of people who are systematically working their way through AtD, with discussion moderated by a different host every week. They're far more comprehensive (and systematic) than I could possibly be. You may want to take a look at their blog and join the discussion. A good place to start is "Baloonacy," one of their earliest posts. It takes a look at Redon's interest in balloons and links to a couple of his works, including "Guardian," as well a drawing of a balloon in flight that does double duty as an enormous eye in the sky.
(To find other posts in this series, type "Bottle Notes" into the box at the top of the page and click "Search this Blog." Use quotes.)