My question is about the horns. With accordance with Lesson 8 if for every Trumpet there are 2 horns required for balance than 4 would be required for 2 trumpets but what we see here is 2 additional Tenor Trombones. But the horns are playing in their lower register which is were I understand they are not very prominent and a bit unfocused. Therefore, is it safe to say that Rimsky followed the formula of 2 trumpets + 2 Trombones and the horns are simply their for added color and Rimsky chose to put them in their weaker register so to not disturb the balance? This also works as a great link to the additional 2 horns + tuba playing an octave below. The 4 horns above smooth out the rougher Tenor Trombones with their warm rounded tone which compliments the rounded bass.
Did I correctly interpret what Rimsky was trying to do or am I completely off the mark? Any other thoughts?
Finally, there is no mention in Lesson 8 about the Bass Trombone does it weigh the same as the Tenor Trombone and can it be doubled with the Tuba or is best to alternate, or use it if a tuba is not available or elsewhere occupied?
I think what is happening here is RK is changing the orchestral colors of the low brass rather than providing a melodic line with the horns.
Glad to see interest in the bass trombone - my instrument. Generally, the range the tenor and bass trombones play are the same, but with a larger bore size, the bass trombone has a fuller sound in it's low register (plus an added trigger so the lower notes can be reached easier) but it lacks some of the brilliance of the tenor trombone in the high registers. I think it is not uncommon for composers to just compose for 3 trombones but modern orchestras interpret trombone 3 to be the bass trombone. I know there are exceptions to this, but this in general. Some composers definately think of the bass trombone as a different instrument than the tenor. I do think of them as separate instruments and it's most noticable when they get doubled. The sounds of two bass trombones at fortissimo sounds like an earthquake to me but when the same players play two tenors the sound is intense but brighter.
"With accordance with Lesson 8 if for every Trumpet there are 2 horns required for balance than 4 would be required for 2 trumpets but what we see here is 2 additional Tenor Trombones."
This is not always true. 2 horns would be required to match 1 trumpet at forte but not at softer dynamic levels such as piano. 1 horn is equal in weight to 1 trumpet, trombone, or tuba being played piano. At forte, 2 horns are equal to 1 trumpet, trombone, or tuba. Hope this helps