He was co-editor with Leon Vashilevski, Dr. Feliks Zaks, and M. Mikhelson of Der arbayter (The worker), Yiddish organ of the Polish Socialist Party (PPS [Polska Partia Socjalistyczna]), which appeared over the years 1898-1906—a total of fifty issues—in London, Cracow, and Warsaw (published in Cracow). The first number (dated December 1898), 16 pp., was published somewhere in Poland by a secret publisher. In 1906 the publication was taken to Warsaw where it was transformed into a weekly newspaper. Horovits also used the name Valetski.
Source: Dr. Y. Shatski, ed., Zamlbukh lekoved dem tsveyhundert un fuftsikstn yoyvl fun der yidisher prese, 1686-1936 (Anthology in honor of the 250th jubilee of the Yiddish press, 1686-1936) (New York, 1937), p. 325.