Final answer:
Mendelssohn's music includes modulation techniques using augmented sixth and Neapolitan sixth chords for transitions to new keys, as well as secondary dominants and enharmonic modulations to remote keys for dynamic shifts within his compositions.
Step-by-step explanation:
Felix Mendelssohn, a composer from the Romantic era, often used modulation techniques in his music, which are key changes that occur within a composition. An example of modulation to a remote key using an augmented sixth chord may involve transitioning from the home key to a new key by way of an augmented sixth chord that functions as a predominant, leading to a dominant chord in the new key. Similarly, a Neapolitan sixth chord modulation typically occurs when the flat second degree of the scale is used in the first inversion to lead into the dominant, thereby facilitating a modulation to a new key.
Regarding secondary dominants, Mendelssohn often employed these to momentarily introduce the harmony of a key other than the home key, creating tension that resolves when the actual dominant of the home key or new key is approached. Enharmonic modulations to remote keys are particularly effective and can be seen in Mendelssohn's compositions, where a single chord is reinterpreted to have a different function, allowing for a smooth transition to a key that would be otherwise distantly related.