sentences:  In all, he had fifteen children, of whom the most famous would be David Seixas, who established the Pennsylvania Institution for the Deaf and Dumb in Philadelphia, and was among the first to discover efficient ways of burning anthracite coal.In 1766, Gershom Mendes Seixas became the leader of Shearith Israel, New York City's first and oldest Spanish and Portuguese (Sephardi) congregation, and remained its minister for about a half century.Although not ordained as a rabbi, Seixas served as hazzan and religious leader to the congregation and was among the first leaders of the Jewish community who had been born and educated in the United States.