College music instructors face an ongoing challenge to provide their students with experiences that will lead to growth in musicianship. An effective means to achieve this growth is through ensemble performance. Such active music making with others is of inestimable value for students who aspire to refine their musical skills. It heightens their rhythmic understanding in its demands for strict synchronization and precise coordination. It also helps shape their aural concepts in its demands for sensitivity to musical line, to clear texture, and to contrasts of dynamics, mood, and style.

In the case of students whose principal performance medium is the piano, the college music teacher would do well to consider the two-piano repertory that developed around Beethoven's time as a serviceable resource well geared to meet many needs in the area of ensemble performance. Beethoven's contemporaries gave considerable attention to the medium, and many of their efforts are worthy of the attention of pianist-teachers.

In the years between 1770 and 1830 at least fifty-six composers wrote such music. The long list of contributors includes the celebrated names of Mozart, Clementi, and Chopin, while conspicuously absent from the list are the names of Haydn, Beethoven, and Schubert, each of whom chose not to write a single original work for two pianos, four hands. Several second-drawer composers like Cramer, Hummel, and Dussek appear on the list, along with a few names so minor that it is difficult, if not impossible, to find their first names.

With such a paucity of major composers contributing to the medium, it comes as no surprise that few two-piano masterworks emerged in those years. Despite that fact, many attractive two-piano pieces did appear, and a look at the developments surrounding the flowering of duo-pianism around Beethoven's time yields some interesting insights into the Classic and early Romantic periods.

To be sure, the first known works written for two performers at two keyboards appeared well before Beethoven's time. Sporadic interest in the possibility of composing such pieces dates as far back as the turn of the 17th century. At that time Giles Farnaby was represented in the so-called Fitzwilliam Virginal Book by a brief piece entitled "For Two Virginals." To date, this remains the earliest known work for two keyboard instruments.

In 1704 the Italian Bernardo Pasquini (1637-1710) wrote a volume of works containing twelve sonatas "A Due Cembali," thought to be for two harpsichords.¹ In France two of the Couperins contributed to the repertory of two-keyboard music. Franis Couperin (1668-1738) published an "Allemande à Deux Clavecins" at the beginning of his "Neuvième Ordre," while his nephew Armand Louis Couperin (1725-1789) wrote two pieces for two harpsichords: "Symphonie à Deux Clavecins" and "Deuxième Quator à Deux Clavecins" in E-flat. Another French composer, Gaspard Le Roux (ca. 1706), wrote six pieces for two harpsichords: "Allemande la Vauvert," "Courante," "Gavotte," "Menuet I and II," and "Gigue." In Germany Johann Mattheson (1681-1764) contributed a "Sonata à Due Cembali" around 1705. Handel is known to have written a "Suite à Deux Clavecins," although only one of the two parts has been discovered.

In the early history of two-keyboard music the Bach family holds a distinguished place. Johann Sebastian composed "Zwei Fugen für Zwei Klaviere" that appear in "Die Kunst der Fuge." His three most famous sons also left works for two claviers. Wilhelm Friedmann (1710-1784) wrote two "Concerti a Due Cembali" in D and F respectively. Carl Philipp Emanuel (1714-1782) composed four "Kleine Duetten für Zwei Klaviere," and Johann Christian (1735-1783) wrote a "Sonata für Zwei Klaviere."

The other composers to be mentioned in the pre-history of two-piano music are Georg Christoph Wagenseil (1715-1777), who wrote a "Duetto in D für Zwei Klaviere," Op. 5; Carl Stamitz (1719-1761), who wrote three sonatas for two harpsichords; Abbe G.J. Vogler (1749-1814), who wrote five sonatas for two keyboard instruments; and Simon Hartmann, who composed in 1777 a "Duo pour Deux Harpes ou Clavecins," Op. 1.

During Beethoven's lifetime the piano rose to first place among keyboard instruments. Numerous journals, diaries, letters, and histories of the time attest to the increasingly prominent role of the piano in the music world, leaving little doubt as to the piano's final eclipse of the clavichord and the harpsichord as the favored keyboard instrument.

As the piano rose in popularity, it became customary to introduce piano music into concert programs that previously had been reserved for orchestral and vocal music. Clementi, Cramer, Czerny, Dussek, Herz, Kalkbrenner, Moscheles, Ries, Steibelt, and Pixis were among the more popular pianists to appear on such programs. Amidst a pianistic milieu, these composers had a natural incentive to write for their own instrument. Accordingly, a profusion of fantasies, marches, rondos, dances, sonatas, variations, and other divertimentos poured from their pens. More than parenthetical to all of this activity was the development of two-piano music.

Although music for two pianos had been written by Müthel as early as 1771, the first public duo-piano performance on record did not take place until March 10, 1784.² At that time Johann Cramer and Muzio Clementi played a "Duetto for Two Pianos" at one of the Hanover Square Great Concerts.³ Clementi had figured also in an earlier, famous, though private, two-piano performance; namely, the friendly "contest of skill" that Emperor Joseph II arranged between Mozart and Clementi at the Court of Vienna in 1781. Mozart describes the occasion in a letter to his father dated January 16, 1782:

After we had stood on ceremony long enough, the Emperor declared that Clementi ought to begin. . . . He improvised and then played a sonata. The Emperor then turned to me: "Allons, fire away." I improvised and played some variations. The Grand Duchess produced some sonatas by Paisiello (wretchedly written out in his own hand), of which I had to play the Allegros and Clementi the Andantes and Rondos. We then selected a theme from them and developed it on two pianofortes.⁴

In the 19th century, two-piano playing became an increasingly popular diversion for musicians and audiences. Frequently at public concerts the guest pianist called upon a colleague to join him in a duet, often at a second piano. Such a collaboration drew warm applause from audiences. The Quarterly Musical of 1822 describes such a response:

The performance which attracted the most notice amongst the few extraordinaries at the benefit was a duet upon two pianofortes by Mr. J.B. Cramer and Mr. Moscheles. . . . The Grand Opera Concert room was filled on the night of Messr. Cramer's benefit, and the duet was the grand object of universal anticipation. . . . In this amicable display of power, both were tasked to the utmost, and so far as public performance (which upon such an instrument must yield in interest to private) could gratify an audience, gratification could not be carried further. The plaudits were long, loud, and universal, while the worthy professors, at the close of the duet, exchanged congratulations with the cordial warmth of mutual admiration.⁵

In 1830 a reviewer in Paris wrote of the appeal that the two-piano playing of Pixis and Moscheles had for the audience gathered at a soirée in the Salons d'Érard: "A duet for two pianos, composed by M. Pixis and performed by Moscheles and the author, gave great satisfaction to the brilliant auditory."⁶ Apparently the excitement generated by seeing two "matinee idols" appearing with one another on the concert platform heightened the already festive atmosphere that permeated some public concerts of the time.

Two-piano playing also occurred at private gatherings. Performers in the public concerts often would gather afterwards for an evening social. On such occasions pianists who were present, professional or amateur, were expected to extemporize—either alone, with a colleague at the same keyboard, or at two pianos. In 1830 Charlotte Moscheles wrote that "at evening parties Moscheles had to endure a great deal of amateur music, and often played as a matter of self-protection, where otherwise he would have declined. On the other hand, he never wearied of making music with his brother artists."⁷ Chopin also describes his participation in such gatherings. In 1829 he writes from Warsaw that "Kessler gives a musical soirée every Friday. Nearly all the artists meet and play together whatever is brought before them 'prima vista'."⁸

Private gatherings of musicians also occurred on a more casual basis. Chopin wrote from Vienna in 1829 that "I became quite intimate with Czerny and often played with him on two pianos. He is a good-natured fellow."⁹ And in 1835 Moscheles was to write of his visit to Mendelssohn's home: "We have had a day of it. First of all I played with Felix Mozart's Duet in D for two pianofortes; and my 'Hommage à Handel.' We then allowed ourselves all manner of musical extravagances; extemporized jointly and alternately at two pianos—an intellectual sort of tournament."¹⁰

In this atmosphere, a considerable body of two-piano music came into being. Much of it is not heard today, nor does it necessarily warrant extensive playing. Then too, much of it is not readily accessible, if at all. The existence of some of the pieces is known only through mentions in contemporary correspondence, periodicals, or catalogues. For the interested reader, a checklist of two-piano music written between 1770 and 1830 is appended.

One of the earliest two-piano pieces from the period under consideration is a "Duetto für 2 Claviere, 2 Flügel, oder 2 Fortepiano" by Johann Gottfried Müthel (1728-1788). Although Müthel was the last pupil of J.S. Bach, it is the influence of Bach's son Emanuel that is noticeable in this work, as in Müthel's other works.¹¹

Written in 1771, Müthel's "Duetto" is in three movements (F-S-F) and abounds throughout with ornamentation of the most detailed kind. This ornamentation may explain why most of the time only one instrument is playing, for the ensemble problems when two performers join in such meticulous music are enormous. Newman describes the effect of such ornamental overload:

But clear contrasts and divisions, other than the breaks between the repeated "halves" of the outer movements, are largely lost in the almost continued atmosphere of highly ornamental, stop-and-go fantasy. . . . Müthel's particular and most frequent method of continuation can be described as a succession of waves formed by the rise and fall of scales, arpeggios, or related figures.¹²

Although the foregoing might discourage the interest of present-day performers in the work, it is worth noting, nevertheless, that Charles Burney found Müthel's works to be "so full of novelty, taste, grace, and contrivance, that I should not hesitate to rank them among the greatest productions of the present age."¹³

In the 1780s both Clementi and Mozart made significant contributions to the two-piano repertory. Among Clementi's 88-odd piano sonatas are two sonatas for two pianos—both in B-flat and both excellent pieces for college pianists. The first, Oeuvre 1, is in three movements and was composed in 1780, while the second, Op. 12, is in two movements and was composed in 1784. Throughout the two pieces, Clementi is careful to give the performers an equal share in the musical responsibilities. There is a good deal of dialoguing back and forth at close intervals of time, throughout which Clementi manages to avoid overlapping registers. In both sonatas the first movements seem to have the least to say melodically, although the other movements of both works have charming melodies that are tastefully embellished. If these pieces do not reveal quite the greatness of depth of the Mozart two-piano works, they are, nevertheless, substantial contributions to our tightly limited repertory of music for two pianos.

One of the high-water marks in two-piano music of the Classic and early Romantic periods—or for that matter, of the entire two-piano repertory—is Mozart's Sonata in D, K. 448, written in 1781 for a performance at the home of Mozart's pupil Fräulein Josephine Aurnhammer, to whom he dedicated the work. In a letter to his father dated November 24, 1781, Mozart describes the circumstances of the first performance: "We [Mozart and Miss Aurnhammer] played a sonata for two claviers, which I had composed expressly for the occasion and which was a great success."¹⁴

That initial success of the work was to continue in subsequent generations. In 1830, for example, the editor of Harmonicon described a performance of the work by Mozart's student Hummel and his partner Moscheles: "In his second concert M. Hummel repeated his concerto, which we heard with increased pleasure. He afterwards played, with M. Moscheles, a duet for two piano-fortes by Mozart, the execution of which was as perfect as was to be expected from two such masters."¹⁵ As has already been mentioned, later in 1835 Moscheles wrote of the great enjoyment he and Mendelssohn derived when playing the work together.

The popularity of Mozart's Sonata in D, K. 448, is understandable from the standpoint of two-piano teams. Mozart integrates the two-piano idiom with the musical content in a seemingly effortless manner. He distributes the musical substance and the musical embellishments equally in the respective Allegro, Andante, and Rondo movements. Lucidity of design, elegance of manner, and appropriateness of performance idiom make the work a musical gem that should be treasured by serious pianist-musicians.

Fortunately, Mozart followed up the Sonata in D one year later with another contribution to the two-piano repertory. This was his Fugue in C minor, K. 426, for two pianos, which he later arranged for string quartet (or string orchestra) and prefaced with a short Adagio for two violins, viola, and bass, K. 546. Einstein speaks of the two-piano work as one

. . . in which he [Mozart] sums up the fruit of his contrapuntal studies and of everything he learned from Johann Sebastian Bach. It is a strict, four-voiced fugue, with a deeply serious, 'dualistic' theme—half imperious and half complaining; and it contains all the devices of inversion and stretto. Only at the end does it assume a more pianistic bearing, but its relation to the 'objective,' contrapuntal portions of the pieces for mechanical organ is unmistakable.¹⁶

In the last decade of the 18th century, Jan Ladislav Dussek (1760-1812) was a major contributor to the category of two-piano music. Although Dussek has aroused considerable interest in recent years as a composer, he still is not as well known as he might be. In the performance realm he has managed to attain recognition for three "firsts"—namely, for being the first to sit during a public performance with his right side to the audience, the first virtuoso to tour in piano performances,¹⁷ and the first to play a six-octave piano in public.¹⁸ He was also the first, in his own music, to indicate pedalings.¹⁹ It is as a composer, however, that Dussek deserves most to be remembered. He merits a not insignificant place in history and even in today's repertory for his sonatas, which are "not only outstanding in quality but the most precociously Romantic sonatas, especially in harmony and keyboard writing, at the outset of the new era."²⁰

Of his numerous piano sonatas, five were written for two pianos. The most accessible today is his Sonata in F, Op. 16, which has been published in a modern edition by Schott (Ed. 10507, 1959). The Sonata is in three movements—Allegro, Larghetto, and Rondo—each projecting a clear, almost textbook example of sonata-allegro, ternary, and rondo form respectively. Within these formal designs, Dussek shows great sensitivity to his medium by distributing musical responsibilities equally between the pianists. Both share equally in the presentation of principal thematic material. The piano figurations that support the piece's melodic structure are sometimes shared antiphonally and other times simultaneously. Broken chords, Alberti basses, broken octaves, and rapid sixteenth-note passages become the property of both pianists at one time or another. The result is a work that engages the sustained interest of performers and listeners alike.

Anton Eberl (1766-1807), an esteemed pianist and composer in his day, had many equally distinguished partners with whom he played two-piano works. Among them was Fräulein Josephine Aurnhammer,²¹ the pianist-composer who also performed on several occasions at two pianos with Mozart.²² During Eberl's concert tour of 1806 through Germany, the young Meyerbeer performed with him Eberl's only known work for two pianos alone, i.e., his "Prelude Suivi de VIII Variations sur la Marche Favorite de l'Opèra Raoul Barbe-Bleue," Op. 31.²³ This piece, like so much piano music of the day, is based on a popular operatic air, namely a march from Grétry's opera.

An ostentatious prelude of thirty-nine measures precedes Eberl's presentation of Grétry's straightforward theme of sixteen measures. Sweeping ascending scales, rapid octaves, and cadenza-like passages lend a bravura quality to this section. Often the two pianists must toss the various musical roulades back and forth so that when a pianistic caper is completed by one pianist, a passage of the same sort will be answered by the second pianist. The musical interest is distributed quite equitably throughout, as though the composer felt that he had to treat the two performers with impartiality. The variations that follow have many brilliant passages of ornamental sixteenth and thirty-second notes. Although the work may well seem cliché-ridden and overly predictable to contemporary ears, it enjoyed great favor in its day.²⁴ A notice in the Allgemeine Musikalische Zeitung two years after Eberl's death acclaimed "these, the last variations he wrote, to be among his best compositions."²⁵

One of the most celebrated two-piano works of the early 19th century appears to have been the "Hommage à Handel," written by Moscheles in 1822. In fact it was the proliferation of such pieces that led Moldenhauer to refer to this period in the history of two-piano music as the "Grand Duo" period: "Virtuosi discovered that playing on two keyboards afforded the chance for much sensational display such as was not possible on a single instrument."²⁶

Also during this time composers occasionally collaborated in the composition of a work. One of the most celebrated products of joint effort is the "Duo Concertante on a March Theme from Weber's Preciosa" by Moscheles and Mendelssohn, which was first performed in 1833. Another similar work is Kalkbrenner's and Dizi's "Grand Duo," Op. 82 from 1827, while the "Grand Duo sur les Marches Favorites d'Alexandre et de La Donna del Lago," Op. 72 by the Herz brothers represents a third collaborative effort.

Whether composed singly or collaboratively, the grand duos hold a certain fascination today, in that they provide another means of understanding the musical taste of the times. Moscheles's "Hommage à Handel," Op. 92, is a case in point. Moscheles described the circumstances that motivated him to write the piece:

I found J.B. Cramer on the point of giving his yearly concert. He showed me the two movements of a sonata which he wished to play with me, and expressed a desire that I should compose a third movement as a finale; only I was not to put any of my octave passages into this part, which he pretended he could not play. I can refuse him nothing. I shall therefore be obliged to strive and write something analogous for him, the disciple of Mozart and Handel.²⁷

In response to Cramer's request, Moscheles wrote an Allegro movement for a finale. Later he added an introduction to the Allegro and published the two components as an independent work, with the title "Hommage à Handel." "Hommage" has an appeal, filled as it is with brilliant passages of rapid arpeggios, scales, and octaves. Unfortunately, these same passages are often rigid in style as well. Its defects notwithstanding, Charlotte Moscheles reported that the first performance of the work created a furor, and the newspapers claimed that it was "an unrivalled treat, an unprecedented attraction."²⁸ To understand the acclaim that the piece received after its performance, it is well to recall that in the London of the 1800s

superficial brilliance was in the air, at least as far as keyboard music was concerned; for the piano—which, with its warm resonance and varied range of tone-color, lent itself more readily to the requirements of facile virtuosity than did the more exacting harpsichord—was by now well established in the public favor, and there was every temptation for the composer to cultivate a showy rather than a serious style of virtuosity.²⁹

It may surprise some readers to find Chopin represented in our segment from 1770 to 1830, yet in 1828 he wrote one piece for two pianos, i.e., the Rondo in C, Op. 73. Chopin originally composed the piece for solo piano in the summer of 1828, but then later in that same year he arranged it in its final form for two pianos. The Rondo was published posthumously in Berlin by Schlesinger in 1855, which accounts for its late opus number.³⁰

Chopin's Rondo towers above the Moscheles and Eberl works in both substance and manner, even though it savors of salon music. But this is salon music of the most tasteful, elegant kind. Chopin opens with an introduction marked Allegro Maestoso in 4/4 meter. Here the first pianist is required to play the more technically difficult sixteenth-note passages, while the second piano punctuates the music with quiet chordal passages. In the rondo that follows, however, Chopin achieves a masterful interplay between the two pianists. The players alternate in the presentation of the principal thematic material and the supporting material, the meter now being 2/4. While one performer plays the principal material, the other plays a filigree that facilitates the limpid unfolding of the musical line. The result is a musical buoyancy, as it were, that does much to give the work its ballast. Chopin's ornaments become integral parts of his musical ideas. They never obstruct the musical train of thought; rather they reinforce it in a stunning way. Even in such a youthful work as this, we find one of the most successful works in the two-piano repertory.

To conclude, we have seen the first major flowering of two-piano music as it occurred in the years between 1770 and 1830. This phenomenon coincided with the emergence of the piano itself. The older harpsichord, with its two manuals, couplings, and registrations perhaps did not suggest the advantages of two individual keyboard instruments playing in ensemble as did the one-keyboard piano.³¹ Moreover, in Beethoven's time music making became a part of bourgeois life. Along with duets at one piano and songs for voice and piano, two-piano music was an ideal manifestation of "house music."

It is quite true that few masterworks for two pianos emerged between 1770 and 1830. With the notable exception of Mozart's contributions, the repertory is more elegant than noble, more brilliant than profound. Nevertheless, the college music teacher can find in this music another point of reference to musical life of the time as well as a valuable resource for ensemble teaching.

 

A CHECKLIST OF TWO-PIANO MUSIC COMPOSED BETWEEN 1770 AND 1830

Titles are abbreviated in some instances and often are translated. When known, dates of composition are given. In some instances approximate dates, based on available dates of other works by the composers in question, are given.

Adam, Louis	Symphonie Concertante, Op. 5 (also 4 hands at 1 piano). Paris, 1787.
Amade, ?	Sonata in A. Leipzig.32
Arnold, ?	Duet in D minor.33
Asioli, Bonifazio	Sonata in F. London, ca. 1805-15.
Berg, George	Duo with Variations, Op. 12. Vienna.
Blaze, H.	2 Duos, Op. 3 (or for harp and piano). Paris.
Bochsa, Robert	3 Duos on Favorite Motifs from Lucia di Lammermoor (or for harp and piano). Paris.
Boieldeau, François	2d Duo (or for harp and piano). Paris, 1796. 4th Duo (or for harp and piano). Paris, 1802.
Candeille, Pierre	Duo, Op. 3. Paris, 1794.
Chopin, Frederic	Rondo in C, Op. 73. Sanniki, Berlin, Paris, 1828. (posth.).
Clementi, Muzio	Sonata in B-flat, Oeuvre 1. Paris, 1780.34 Sonata in B-flat, Op. 12. London, 1784.
Cramer, Johann B.	Grand Duo, Op. 24 (or for harp and piano). Paris, Vienna, 1806.
Czerny, Carl	Grande Polonaise Brillante, Op. 18. Vienna, ca. 1821.
Dalvimare, Martin	Duo, Op. 22 (or for harp and piano). Paris. 2d Duo, Op. 31 (or for harp and piano). Paris.
De Pinna, Joseph	Duet. London, 1824.
Dussek, Jan Ladislav	Duo, Op. 36 (or for harp and piano). Paris, 1794. Duo, Op. 11 (or for harp and piano). Paris, 1795. Grand Duo, Op. 38 (or for harp and piano with horns, ad lib.). Vienna, 1798. 2 Easy Duos (or for harp and piano). Vienna, 1808.
Eberl, Anton	Prelude and 8 Variations on a Favorite March from Raoul Barbe-Bleue, Op. 31. Vienna, 1804.
Ferrari, Jacopo	Duo, Op. 13 (or for harp and piano). Paris, 1794. Duo, Op. 20 (or for harp and piano). Paris, 1795.
Goubau d'Hovorst, Leopoldine	Grand Sonata, Op. 14. Vienna.
Greulich, Charles W.	Grand Divertissement, Op. 23. Leipzig.
Herz, Henri	Variations et Rondeau Brillant, Op. 16 (or for harp and piano). Bonn, Leipzig, ca. 1825.
Herz, Henri and Jacques Simon	2d Grand Duo Concertant, Op. 72. Vienna.
Himmel, Friedrich	Grand Sonata. Leipzig, 1801. Écossaise. Berlin, ca. 1814 (posth.).
Hummel, Johann N.	Introduction et Rondeau, Op. 5. Leipzig (posth.).
Ilinsky, Jean-Stanislas	Duo Concertante, Op. 11. Vienna.
Jadin, Louis	Grand Duo (or for harp and piano). Vienna. Fantaisie (or for harp and piano). Paris.
Kalkbrenner, Friedrich	Marche (or for harp and piano). Leipzig, 1827. Concerto for Two Pianos, Op. 125. Leipzig. Grand Duo, Op. 128. Leipzig.
Kalkbrenner and Dizi, François Joseph	Grand Duo, Op. 82 (or for harp and piano). Vienna, 1827.
Karr, Henri	Grand Duo, Op. 15 (or for harp and piano). Paris.
Kleinheinz, Franz	Grand Sonata, Op. 14. Vienna, 1804.
Lechopié, Pierre-Martin	Duo (or for harp and piano). Paris.
Leidesdorf, Maximilian	Duo, Op. 91 (or for 2 harps). Vienna, 1805. Grandes Variations, Op. 158. Vienna.
Lemoine, Jean Baptiste	Duo, Op. 16. Paris.
Lickl, Jean-Georges	Grande Sonate Brillante, Op. 30. Vienna, ca. 1828.
Lindpaintner, Peter Josef	Divertissement. Leipzig, 1818.
Marin, Marie-Martin	Duo, Op. 17 (or for harp and piano). Paris, 1803.
Méhul, Etienne	Duo. Paris.
Moscheles, Ignaz M.	Grand Duo Concertant in A. Vienna, 1814. Hommage à Handel. Vienna, 1822.
Mozart, Wolfgang A.	Sonata in D, K. 448. Vienna, 1781. Fugue in C minor, K. 426. Vienna, 1782.
Müthel, Johann Gottfried	Duetto für 2 Claviere, 2 Flügel oder 2 Fortepiano. Leipzig, 1771.
Pixis, Johann Peter	Grandes Variations Militaires, Op. 66 (with orchestra ad lib.). Leipzig, Lyons, Paris. Rondeau Hongrois, Op. 33. Vienna, Paris. Variations Brillantes, Op. 112. Paris?
Pleyel, Ignaz Joseph	Duo, Op. 50 (or for harp and piano). Paris, 1796.
Pollini, Franz	Grande Sonate, Caprice, et Variations (or for harp and piano). Mailand, 1807.
Pradher, Louis-Barthelemi	Rondeau, Op. 19. Paris, 1823.
Ries, Ferdinand	Introduction et Rondeau, Op. 57 (or for harp and piano). Paris, ca. 1815. Grand Duo (or for harp and piano). Paris. Sextet, Op. 142 (or for harp and piano with clarinet, horn, bassoon and contrabassoon, ad lib.). Mainz, Paris, ca. 1826.
Rigel, Henri	Duo, Op. 25 (or for harp and piano). Paris. Duo sur des Airs d'Armide et de Télémaque (or for harp and piano). Paris. Duo. Paris.
Rummel, Charles	Rondeau en Forme de Valse, Op. 66. Paris, 1829.
Saujon, ?	Fantasie (or for harp and piano). Paris.35
Schloer, ?	Duo (or for harp and piano). Paris.36
Schloer and Ancot, ?	Air Varié avec Introduction et Finale. Paris.
Schmitt, Aloys	Konzertstueck für Zwei Pianos, Op. 23. Berlin?
Schneider, Friedrich	Six Grandes Polonaises, Op. 23. Leipzig.
Steibelt, Daniel	Sonata, Op. 36 (or for harp and piano). Leipzig, ca. 1800. Grand Duo (or for harp and piano). Leipzig, 1802. Duo (or for harp and piano). Leipzig, 1806. Duo (or for harp and piano). Leipzig, 1809. 2 Duos (or for harp and piano). Leipzig.
Stunz, Joseph	Variations, Op. 9.37
Wolfl, Josef	Duo, Op. 37 (or for harp and piano). Paris.
Worzischek, John H.	La Sentinelle, Divertissement, Op. 6. Vienna. Grande Ouverture, Op. 16. Vienna, 1823.

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¹William S. Newman, The Sonata in the Baroque Era (3rd ed.; New York: W.W. Norton, 1972), p. 160.

²Arthur Loesser, Men, Women, and Pianos (New York: Simon & Schuster, 1954), p. 241.

³Ibid.

⁴Emily Anderson (ed. and trans.), The Letters of Mozart and His Family (3 vols.; London: Macmillan, 1938), III, 1180-81.

⁵"Sketch of Music in London," Quarterly Musical Magazine and Review, IV/14 (1822), 260-61.

⁶"Concerts at Paris," Harmonicon, VIII (March 1830), 115.

⁷Charlotte Moscheles, Life of Moscheles, with Selections from His Diaries and Correspondence, trans. A.D. Coleridge (2 vols.; London: Hurst & Blackett), II, 251-52.

⁸Moritz Karasowski, Frederic Chopin: His Life and Letters, trans. Emily Hill (3rd ed.; London: W. Reeves, 1938), p. 114.

⁹Ibid., p. 108.

¹⁰Moscheles, I, 329.

¹¹William S. Newman, The Sonata in the Classic Era (2nd ed.; New York: W.W. Norton, 1972), pp. 437-38.

¹²Ibid., p. 439.

¹³Percy A. Scholes (ed.), Dr. Burney's Musical Tours in Europe (2 vols.; London: Oxford University Press, 1959), II, 240.

¹⁴Anderson, III, 1161.

¹⁵"M. Hummel and His Two Concerts," Harmonicon, VIII (June 1830), 264.

¹⁶Alfred Einstein, Mozart, His Character, His Work (New York: Oxford University Press, 1945), p. 273.

¹⁷Harold C. Schonberg, The Great Pianists (London: Victor Gollancz, 1964), p. 58.

¹⁸Ibid.

¹⁹Ibid.

²⁰Newman, The Sonata in the Classic Era, p. 439.

²¹Anderson, III, 1069.

²²Ibid., 1161, 1179, 1201, 1236.

²³A. Duane White, "The Piano Works of Anton Eberl (1765-1807)" (unpublished Ph.D. dissertation, University of Wisconsin, 1971), p. 214.

²⁴Ibid.

²⁵Ibid.

²⁶Hans Moldenhauer, Duo-Pianism (Chicago: Chicago Musical College Press, 1950), p. 73.

²⁷Moscheles, I, 64.

²⁸Ibid., 64-65.

²⁹Kathleen Dale, "The Three C's: Pioneers of Piano Playing," Music Review VI/3 (August 1945), 140.

³⁰Maurice J.E. Brown, Chopin: An Index of His Works in Chronological Order (New York: Macmillan, 1966), p. 26.

³¹During Beethoven's lifetime the widespread use of the duet led to the invention of a special pianoforte fitted with two separate keyboards and actions placed opposite to each other within a single case. See Rosamond E.M. Harding, The Pianoforte: Its History Traced to the Great Exhibition of 1851 (Cambridge: Oxford University Press, 1933), pp. 105-17.

³²See C.F. Whistling, Handbuch der musikalischen Literature (reprint of the 1828 vol.; Georg Olms: Hildesheim, 1975), p. 514.

³³Charlotte Moscheles, I, 100.

³⁴See Alan Tyson, Thematic Catalogue of the Works of Muzio Clementi (Tutzing: Hans Schneider, 1967), pp. 34-35.

³⁵Whistling, p. 517.

³⁶Ibid.

³⁷Ibid.