This second movement represents the metronome. Please keep in mind that the music in this movement represents the mechanical, wind-up metronome that is very different than the modern-day digital metronome. Because it uses a pendulum, the metronome is very sensitive to the surface it is on. If it is slightly uneven, the ticks of the metronome will be erratic. Tempo was determined by the position of the weight on the pendulum. Since the metronome was wound using a spring mechanism, it tended to get slower as the spring tension decreased.
The music of the section that goes through measure 37 represents metronome practice. This section consists of constant eighth notes for 33 measures. While the rhythm is static, being in 2/4 with an occasional 3/4, the tempo, melodic line, harmony, and dynamics are varied. Imagine someone practicing a passage with a metronome and gradually increasing the tempo until the tempo gets so fast, the musicians goofs up. Measures 34-37 represent the frustration of the musician when he/she can't keep up with the metronome.
At measure 38, the musician goes back to practicing slower, but as he/she practices, the metronome begins to wind down and get slower. At measure 62, the tempo is so slow that the uneven surface the metronome is on begins to make the metronome beat unsteadily. The movement ends with the metronome stopping completely.
In keeping with the double meaning of the word invention, there are sections of tight imitation. An example would be measure 23-24 where the trombone lead is followed by the Horn a fifth above an eighth note later and then the trumpet at the octave an eighth note later than the Horn.
Below is the transposed score and sampled sounds in video format. Your comments are always welcomed.