Via ScienceDirect / Historia Mathematica : 1) A Euclidean proof for the Fourth Postulate : buff.ly/1anVGQd 2) There is no Euclidean proof of the fourth postulate : buff.ly/AeXC5T5 3) There is no obstruction to a Euclidean proof for the fourth postulate : buff.ly/EK6rk5K #mathematics #math #maths

Call for applications, free school on Arabic-Islamic Astrolabes at the Institute for the History of Arabic-Islamic Sciences in Frankfurt; March 23 workshop for experts, March 24-26 classes for advanced students. Classes in English, details below; apply by January 15th, 2026. #HistSTM #MedievalSky

Fact-checking Netz's mischaracterisations of Kuhn and Koyré: intellectualmathematics.com/blog/netzs-f...

Drawing a circle with a rope. digi.vatlib.it/view/MSS_Vat...

Much of Euclid’s Elements is easily misunderstood. Some proofs seem to have logical gaps. Some constructions seem pointless, others seem needlessly convoluted. Each of these provides a window into how the ancient Greeks thought about math and the philosophical role that geometry played.

My new article, on why Euclid had to postulate that all right angles are equal: www.sciencedirect.com/science/arti...

Viktor Blåsjö's review of the book "Form & Number: A History of Mathematical Beauty" by Alan J. Cain, is now live at tug.org/books/review...

What is mathematical beauty? tug.org/books/review...

My obituary of Henk Bos, who opened the eyes of so many of us to the history of mathematics: research-portal.uu.nl/ws/portalfil...

I believe Aristarchus did not make a "lousy measurement" (15:58). Rather, he deliberately underestimated the size of the sun, and showed that even in this worst-case scenario it is way bigger than the earth (i.e. heliocentrism wins). See arxiv.org/abs/2102.06595 §7.6.

I like this rant: I never found Gabriel's horn / Torricelli's trumpet to contradict my intuition, though it's a fun example. https://intellectualmathematics.com/blog/torricellis-trumpet-is-not-counterintuitive/

ICYMI there's a new episode of @viktorblasjo.bsky.social's podcast out this week, first new episode in over a year. A fun listen as always

Today I learned (ht Viktor Blasjo) how Huygens summed the reciprocals of the triangular numbers. He regrouped the series and showed that it equals the geometric series 1+1/2+1/4+... = 2, like so!

New Medieval Books: The Optics of Ibn al-Haytham Books IV-V www.medievalists.net/2024/08/new-... #books

My book in the Cambridge Elements series on "Mathematical Rigour and Informal Proof" is out today! It's free to download for two weeks, so please share it widely with anyone who may be interested. 🥳🎉 www.cambridge.org/core/element...

🥁: Historian of mathematics, famous contrarian and "Intellectual Mathematics" podcaster @viktorblasjo.bsky.social is now on Bluesky! #histsci