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« Shadowlands in the History of Technology--the Sewing Machine, ca. 1838 | Main | Wings Taking over Prayers: Human Flight in 1714 »


Aaron Kralik

Helium is becoming rather scarce once again. I remember reading a while back that we were pretty much out of the stuff (helium on earth is a byproduct of radioactive decay and what little we have has accumulated over eons)and once we are out, we are out.

Nancy Ellis

I've been following your blog for several weeks now and I'm glad that I found it: I learn something w/ each of your posts and, even better, what I learn usually sparks a direction of inquiry for me to follow. I'm enjoying keeping my brain limber! Thank you.

Jeff Donlan

I think hydrogen is not quite an explosive in the way we usually think of explosives (TNT or little blobs of plastic explosive used by bad guys and the men who defeat them). It burns hotly in the presence of oxygen, releasing a lot of energy. If confined, it may well explode out of its confines. The hydrogen in the Hindenburg burned impressively but did not explode anything. And that satisfies my daily need for pickiness.

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