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169

Euler did write this, but it was not a mistake! Euler's statement was correct under his own definition of the notation that he was using. I looked at the PDF version of Elements of Algebra linked to in SCappella's answer. Reading Section I, Chapter XIII, I found that Euler wrote that most numbers have two square roots, which matches the definition of the ...


147

The Romans built the aqueducts -- as well as bridges, piers, and colossal buildings -- out of concrete. Stone and brick were usually just exterior casings for the concrete structural core. And the secret of super-durable Roman concrete was indeed lost for centuries. Modern concrete uses a paste mixture of water and Portland cement (a fine powder made from ...


84

The Twitter thread gives an explicit source for this letter, 'A Reluctant Icon: Letters to Neil Armstrong'. by James R. Hansen. This book exists, from Purdue University Press, ISBN 9781557539694 The publisher's blurb says: Artfully curated by James R. Hansen, A Reluctant Icon: Letters to Neil Armstrong is a companion volume to Dear Neil Armstrong: Letters ...


34

The knowledge of how to build aqueducts was not lost. See Vitruvius and Frontinus among other texts. Some few techniques that were more practical knowledge among workers might not have been written down, though. Musk is totally wrong here. The real reason people after the Romans didn't build aqueducts is not that they couldn't. It's because if you don't ...


24

Euler did argue that √-2 √-3 = √6. Whether this is a mistake depends a lot on context. This appears in Euler's 1770 publication Elements of Algebra in Section I., Chapter XIII. (pdf link). Moreover, as √a multiplied by √b makes √ab, we shall have √6 for the value of √-2 multiplied by √-3; and √4, or 2, for the value of the product of √-1 by √-4. Thus ...


20

For the US, we have pretty detailed record keeping of how many slaves were imported, but for North Africa we do not. The number of African slaves imported to the US is about 300,000, only a fraction of the approximately 12.5 million that were brought to the Americas in total. As for the number of white slaves brought to North Africa, it depends on whose ...


18

This answer focuses specifically on Queensland's capital Brisbane, since its history is best documented, but the general principles would have applied to other towns as well. 1) Is it true that these streets were used to curfew indigenous Australians? Yes, it is -- but the naming predates the policy. More specifically, boundaries were defined to set the ...


17

@hdhondt's comment on the question made me aware that I totally missed the image is embedded in a thread and it's about the book "A Reluctant Icon: Letters to Neil Armstrong" . It seems the letter of the teacher is from 2000, so Neil does indeed mean the Internet. That makes the whole story quite plausible.


8

John Brown was a militant abolitionist. He led a militia in the "Bleeding Kansas" crisis - a conflict over the question whether the Kansas territory will allow slavery or not. He later organized the Harpers Fairy raid, an attempt to initiate a slave rebellion in the South. Wikipedia has a well sourced article on the funding of the raid which lists ...


6

Your question seems to assume that all the people who died during the genocide were born during that time period, but I don't see why that's necessarily true. The numbers that are asserted are that the population was on the order of 20 million prior to the genocide, and 10 million afterwards (40 years later). Furthermore, the debate seems to be less over ...


6

As a partial answer, according to the 1987 book Systems and Theories of Psychology, volume 2, page 410: We conclude our discussion of the Stroop effect with a story for whose veracity we cannot vouch. It seems a man was accused of being a Russian agent, a charge which he vehemently denied. He claimed to know nothing even of the Russian language. His ...


6

The story seems plausible, except that this was a mob lynching, not anything ordered by Mao. The story originates from Alfreda Murck, "Golden Mangoes—The Life Cycle of a Cultural Revolution Symbol" Archives of Asian Art (2007) 57 (1): 1–21. Getting a glimpse, the boy thought the fruit looked like a somewhat shriveled sweet potato. He went home ...


4

Similar statements are in Ricardo's obituary in the Sunday Times on 14 September 1823 and Paul Samuelson's more recent articles about Ricardo. This story might be described as mythical and also involves some confusion between David Ricardo and Nathan Rothschild, also supposed to have made a large fortune over news from Waterloo, especially as one of the ...


4

A famous practical example was found in WWII prisoner of war camps where cigarettes became a de-facto currency. This happened without any central organisation or planning; prisoners started with barter, and over time found that cigarettes had become the medium of exchange because they were more-or-less fungible, small and common enough to buy small things ...


2

Latest date and not the same claim, but... quote from Meet the Sole Employee of the U.S. Metric Program: As the years went on, the Metric system wasn't only derided as confusing. It was a communist conspiracy! If the Americans converted under a multi-million dollar price tag, it was prime time for the Soviets to invade our weakened economy, according to the ...


2

The answer beginning, "Suppose that A and B exchange with each other" is unreferenced and factually inaccurate. The story being told in that answer has been known to be false for 100 years. Here is a constructive critic of Graeber affirming this: As Graeber explains, however, pure barter as such never existed. The myth of barter is a handy story ...


1

What made me suspicious is the phrase "Or you could get on the net and find …". There's no date, the letter could be from a time when the Internet did exist but the whole "feeling" of the letter makes me think it was written a few years after Apollo 11, at the latest The Tweet has not provided you the letter to which Armstrong was ...


1

My take on this is that it's a misunderstanding based on the Protestant numeration of the 10 Commandments. The original commandments given to Moses, which number 17 or more distinct commands, were not numbered the "10 Commandments" as they are known today until many centuries after they were written down. The Catholic (and Lutheran) numeration of ...


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