Chapter 1: Section 5: Page 36: Lines 8-9 (590-591)

 "Broke these in on the Ferris wheel," he said, "but couldn't figure out how to compensate for the movement. Gets blurry and so forth."

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"Ferris wheel"
The Ferris wheel was introduced at the Chicago World's Fair. Apparently it wasn't the first "sit on a wheel and go up in the air" amusement ride. But it was inarguably something completely different based on the size and scale.

The Chicago World's Fair Ferris wheel was 264 feet high. Each compartment could hold up to sixty people. And the ride took 10-20 minutes. I don't know why there's such a huge difference in the estimated time for a ride! Did the wheel have different settings to speed it up or slow it down depending on how many people were waiting to spend their fifty cents on it? Apparently, according to Lew here (the "spotter"), it moved fast enough so that his telescope constantly lost focus of the area he was observing. It's sort of the same principle as to why you can't write an accurate book about the entire 19th century. You have to focus on a smaller area and then spend 1000 pages detailing what you see. Because the movement of history makes things blurry and so forth.

"couldn't figure out how to compensate for the movement"
Imagine all the people who read this line and just move quickly past it. Imagine how blurry the entire text becomes when the reader moves past every line at the same speed. How do you compensate for that as an author?! You probably begin your novel with the line, "Now single up all lines!"
    That wasn't what I was going to say about this. I really wanted to talk about movement and telescopes. I had a backyard telescope that I used often in my late teens and early twenties. It was powerful enough to see some of the moons of Jupiter (as dots and shadows on the planet! Not in great detail!). I wasn't on a Ferris wheel but I, too, had to compensate for movement of the Earth (but not for focus, of course. You know how Lew could have compensated for movement that wouldn't have caused what he was looking at to go blurry? Look out of the side window of the Ferris wheel and not the window that aligns with the wheel's movement!). The telescope had a flexible tube sticking out of it with a dial on it that you would twist as you were observing some far off celestial object so that it wouldn't disappear from your view as the Earth rotated. It's hard to keep something so far away in such a small frame!
    The difficulty of observation in these cases is that both the observer and the observed are in constant motion. History can be viewed in the same way if we realize that our beliefs and attitudes, ethics and moralities, change drastically across time. So a historian of the 1890s writing in the 1940s would come to drastically different conclusions because their focus would be completely different. And the further we get away from the 1890s in time, the less detail we can make out. But we're also observing it with totally different instruments (i.e. our modern perceptions).