What is going on in that score fragment?

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Heh heh!

Any of you who have had a little musical training know that most of the time, music is written in four parts (or fewer).  In the Mendelssohn Octet, of course, there are eight instruments, and what could they all be doing, considering that an ordinary chord only has three notes, and in 4 parts, one of those (at least) is doubled, usually at an octave.  So I thought I'd make things a little more transparent by showing you what's going on in just these first several bars!

Three of the instruments are just alternating notes.  This adds nothing to the harmony, but it does add to the texture.  It's a little like strumming a guitar in a pop song; you get a certain rhythmic excitement out of it.  (In a classical ensemble, without a set of drums, you can imagine that every bit of rhythmic support is well appreciated.)

The lowest part is Cello 2, which simply holds a low E Flat.  The whole tune starts off, and stays in, E Flat for a couple of bars, so that makes sense.  I'm not going to give you that note separately.

The second lowest part is cello 1, which alternates E Flat and B Flat.  (The E Flat chord is -- going from the bottom -- E Flat, G, and B Flat, but of course you can add as many octaves of these as you like.)  Here it is:

This produces a sort of sawing sound that you can hear if you listen carefully!

Meanwhile, violins 2, 3 and 4 are doing the same sort of thing, producing a rather frantic alternating chord.  ("4 Violini" simply means four violins, and "Cresc." is short for crescendo : getting gradually louder.)

The violas, not to be left out, are playing a sort of syncopated 2-note chord:

The First violin plays the melody we hear most prominently.  I really don't need to present the whole thing, which you can hear here.

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