Engaging with the natural notes of the (French) horn. 

Currently there are educational videos as well as videos for playing along with. Duets, trios etc minus a part so that the experience of playing just intonation intervals can be somewhat 'live'.  The first in the series invites you to join me in a duet. Use the harmonics of the horn to achieve simple just intonation in a few standard chords in C major (concert F). Fingerings are suggested and the notation shows the major 3rds that should be narrower than standard 12-tone equal tempered intervals. Notation uses the Extended Helmholts-Ellis Just Intonation system devised by Marc Sabat & Wolfgang von Schweinitz (see their detailed explanation at https://marsbat.space/pdfs/notation.pdf). The video is embedded below for easy access.

There will be a book published at some time in the future. There's a sample below this section, called French horn Made Simple.

Some of the videos below have been renamed and are in the playlist Tuning the Horn https://youtube.com/playlist?list=PLj-3CaGOcPF0PYFll2X_gd7T8Yjb80v1p . They are for advanced players wishing to expand their knowledge, experience and skills. 

Overview - embedded below  

3rd harmonic - https://youtu.be/Ur-WWNJARL0 

5th harmonic - https://youtu.be/Yz9anwRH_1M 

7th harmonic - https://youtu.be/YDjYnxAs6Ck 

11th harmonic - https://youtu.be/Jp1qaHl5b0g 

13th harmonic - https://youtu.be/PLnf0lW3XOs. 

Practical exercises: 

7th harmonic - https://youtu.be/TPmVYGvXJ2s 

11th harmonic - https://youtu.be/0KHtVSxlXI0 

13th harmonic - https://youtu.be/Yb1ugIlY6v0