On the home page of I referred to the hand in the bell.

View one (of three possibilities of Baroque horn playing hand use):
Most baroque players in mainland Europe play baroque horn with hand technique, preferring it over the definitely not historical use of vent holes. Stuff like Bach cantata 105 is way to difficult to try without either.

View two:
The hand is out of the bell, but ventil holes are added to the horn to be used like flute holes, that adjusts the tuning on tones that are out of tune with the temperaments of the day. There is no proof of this at all from authentic baroque horns. This is common in England, and some in Canada.

View Three:
The Horn has been played with the hand in the bell since the end of the Baroque era. Before about 1760, the hand was not used in the bell, nor were there holes in the horn to help with the pitch of the difficult tones.
We are forgetting that 60 years ago it was quite common for orchestra string sections to play quite out of tune, Dennis Brain revolutionized horn playing with accurate musical performances. Now we have hand held tuners that have vastly improved the quality of music, at least regulated musicians towards a greater prevalence of equal temperament.
An F a quarter step sharp in passing to notes quite well in tune, or a high A a 3rd step flat in was not that out of tune, because the refined tuning wasn't like what we expect. How many people complain today that equal temperament sound out of tune? I do? It's like that. The horn was played close to in tune where possible, but there are some funny notes on the instrument with the bell up and hand out of the bell! The funny note can be played lightly, de-emphasising the problems.

The most authentic horn recording I have heard will be posted here soon . (Well maybe)