© Robert W. Eshbach, 2013
When he was not roughhousing at home with the Wittgenstein children, Joseph seems to have spent the majority of his social time in the company of adults. Occasionally, we learn of his having formed friendships with boys of his own age, such as Fanny Hensel’s son, Sebastian, or Ignaz Moscheles’ son Felix; how close these friendships were, however, is difficult to tell. Sebastian Hensel lived in Berlin, and though Joseph and Felix Moscheles had been acquainted in London, Felix would not reside in Leipzig until 1846, when his father, Ignaz, took up his piano teaching duties at the Leipzig Conservatory. 
Joseph found a close friend in Otto Goldschmidt, the son of a Hamburg merchant who was Louis Plaidy’s piano student at the Conservatory.  Goldschmidt was several years older than Joseph, but of a similar Jewish background, and a good musician. Like Joseph, he studied counterpoint with Hauptmann. In later years Goldschmidt had a significant musical career in England, but he is perhaps best known today as the husband of Jenny Lind, whom he married in Boston while accompanying the “Swedish Nightingale” on an American tour.
At the end of May, 1845, Joseph and Otto found a new friend in the 22-year old William Smith Rockstro,  an English protégé of Sterndale Bennett, who had come to study at the Conservatory. Like Goldschmidt, Rockstro joined Plaidy’s piano class, and studied counterpoint with Hauptman. Though Joseph was not yet fourteen, he and Rockstro formed a friendship that would be strengthened later that autumn, when Mendelssohn returned from Frankfurt and accepted both Rockstro and Goldschmidt into his select class of seven students in piano interpretation and composition.
Since the days of his friendship with “Mundi” Singer in Buda-Pest, we have no indication that Joseph had enjoyed an intimate friendship such as he now had with his two older companions. Sir Charles Villiers Stanford recalled:
[Rockstro] told me that there were three of them always together — Joachim, Otto Goldschmidt, and himself — and that this trio used occasionally to become a quartet by the advent of a fourth brilliant boy who was studying law, which he used to lay down so dogmatically that Joseph and he sometimes nearly came to blows […]. The occasional visitor was Hans von Bülow, and much as they admired each other’s genius, they always went on in the same way; Hans taking an impish delight in treading upon a tender toe, and Joseph just letting him go as far as he dared, but no farther. Their immense sense of humour, however, generally saved the situation. [i]
Rockstro […] described to me how [Joachim and Goldschmidt] used to have internecine encounters, which they sank when v. B. appeared on the scene to stay with his relative, Frau Frege. They joined forces to defend themselves from v. B.’s satirical tongue, and gentle Rockstro had to pour such oil as he could upon the troubled waters. They were all then in short jackets, but they managed to make it appear that their coats had tails to tread on. Joachim and v. B. were the protagonists. The boys were fathers to the men. They kept up their altercations of squabbles and reconciliations to the end of their lives. The most serious breach was after the Weimar manifesto, when v. B. (as he afterwards confided to Joachim in an affectionate moment) considered the advisability of purchasing a pistol to shoot him at sight. But they had a deep underlying respect and admiration for each other, though their natures were so diverse as to make frictions unavoidable. He never stinted in his praise. Joachim rarely expressed his. Therein lay the kernel of the whole matter. The one pined for outspoken appreciation, which the other never volunteered. [ii]
Otto Goldschmidt and Jenny Lind
 “When […] we met in Leipsic [in 1846],” Moscheles writes in his Fragments of an Autobiography, “it so happened that I was suddenly fired with the desire to play the violin too. My friend Joseph was quite ready to teach me, and we started operations, but two or three lessons were sufficient to convince him and me, that mine was an unholy desire, which, if gratified, would give me the power of inflicting much suffering on my fellow-creatures, and which therefore was calculated to lead me into trouble. So we gave it up, and Joachim has had to rely on other pupils for his reputation as a teacher.” [Moscheles/FRAGMENTS, p. 25.]
 Otto Moritz David Goldschmidt (1829-1907) attended the Leipzig Conservatory from 1843-1846. In addition to his studies with Plaidy and Hauptmann, he was a member of Mendelssohn’s elite piano class. He married Jenny Lind in 1852, and thereafter was often associated with her in musical projects and public performances. Goldschmidt converted to the Protestant faith, and was active as a church musician in England. He became professor of piano at London’s Royal Academy of Music in 1863, and was vice-principal of the same institution from 1866-1868. He composed a variety of works, including the 1867 oratorio Ruth, written for his wife.
 Born William Smyth Rackstraw (1823-1895), Rockstro attended the Conservatory for only one year: from May 1845 to June 1846. Like Otto Goldschmidt, Rockstro would go on to an unusually prolific and varied career in England as a composer, pianist and organist, editor and author. He was known in his time as a leading authority on early counterpoint, and an expert on the music of Palestrina, whose music he ws said to be able to imitate with confounding fidelity. He wrote A General History of Music, biographies of Handel and Mendelssohn, and with Scott Holland, a biography of Jenny Lind.
[i] Stanford/MEMORIES, pp. 133-134.