diff --git a/free-science-books.md b/free-science-books.md
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 * [GRE Physics Test Practice Book](https://www.ets.org/s/gre/pdf/practice_book_physics.pdf) - (PDF)
 * [Introduction to General Relativity](http://www.staff.science.uu.nl/~hooft101/lectures/genrel_2013.pdf) - Gerard ’t Hooft (PDF)
 * [Introductory Physics I - Elementary Mechanics](https://webhome.phy.duke.edu/~rgb/Class/intro_physics_1/intro_physics_1.pdf) - R.G. Brown (PDF)
-* [Motion Mountain Physics](http://www.motionmountain.net/)
+* [Motion Mountain Physics](http://www.motionmountain.net) - Christoph Schiller
 * [Physics Before and After Einstein](http://www.dmi.unipg.it/mamone/pubb/PBAE.pdf) - Marco Mamone Capria (PDF)
 * [Physics Test Practice Book](https://www.physics.ohio-state.edu/undergrad/greStuff/exam_GR9677.pdf) - (PDF)
 * [Problems in Introductory Physics](http://www.lightandmatter.com/problems/problems.pdf) - B. Crowell and B. Shotwell (PDF)