Round Earth

Well, Bright Earth has led me to Round Earth as a result of researching the relationship of the bluish-green ice falls cascading from the rock cliffs along I-89 that were extremely numerous yesterday.

The previous day I had read the section in Bright Earth about how glass might have been discovered, learning that clear glass is harder to make than colored simply because "natural" glass contains impurities that often give a bluish-green cast. Aha! Is this cause the same as that which creates the bluish-green ice? What's in the glacial silt that is common in glass? Haven't finished yet--more later.

BUT, I did stumble across this article on the how the fact that the earth is round can be determined from a ship's wake. My immediate interest in this stems from the time I was taking classical Greek and became fascinated by the science of the early Greeks. I remember, on a full moon night, using trigonometry against the vertical side of brick building to determining the distance of the moon from the earth. I was close, maybe off by 20,000 miles.

There's a lot of math in the linked article, but the salient parts are the Introduction on p. 1, the magnificent image on p. 2, and the Conclusions on p.4. The simplicity of the reasoning is stunning. Worth taking a skim at.