Page 5
https://www.youtube.com/watch?v=oIOLFeCo7-0&t=1s

Page 20
https://www.hydro-international.com/content/article/promising-future-for-hydrography

Page 22
https://www.hydro-international.com/content/article/the-pressure-beneath-the-surface

Page 33
https://moruroa-files.org/fr/ declassified-documents
https://moruroa-files.org/documents/04-18-94

Page 42
https://commons.wikimedia.org/w/index.php?curid=5295485
https://arkivo.esperanto-france.org/divers/unuakong/rollet/pk_1k360.gif
https://gallica.bnf.fr/ark:/12148/bpt6k1178874w/f175.item

Page 43
https://commons.wikimedia.org/w/index.php?title=File:Zamen-hof_1912.jpg&oldid=1015431755
https://commons.wikimedia.org/wiki/File:Rollet_de_ l%E2%80%99Isle_-_Provo_de_Marista_Terminaro,_1908.pdf
https://eo.wikipedia.org/wiki/Dosiero:Robert-RolletdelIsle.jpg

Page 44
https://commons.wikimedia.org/w/index.php?title=File:Esperanto-konferenco_Locarno_1926.jpg&oldid=1043337792
https://bitarkivo.org/gazetoj/bultenoisae

Page 45
https://alex.onb.ac.at/cgi-content/anno-plus?aid=e3s&datum=1934&pos=133&size=45

Page 52
https://e.pcloud.link/publink/show?code=XZ3cwwZX24EN8vKLtSWxKr3TMfLqb6fMMT7