Jan van Kessel the Younger are attributed about 200 small still lifes produced in Southern Europe in the late 16th and early 17th century. Jan van Kessel the Younger's small known authentic oeuvre is different in style and execution and substantially higher in quality than the works, which have now been attributed to Pseudo Jan van Kessel the Younger. His portrait style was described by his contemporary Antonio Palomino as very close to that of his fellow Flemish painter Anthony van Dyck. Van Kessel was a specialist of the genre of group portraits. An example is the "Portrait of a family in a garden" in
Cornelius Van Alen Van Dyck which later became the American University of Beirut. He also taught astronomy in its literary section, directed its observatory and meteorological station as well as the mission press, and edited its weekly journal al-Nashran. He wrote Arabic textbooks on chemistry, internal medicine, physical diagnosis, and astronomy, publishing some of them at his own expense. He translated al-Razi's ninth-century treatise on smallpox and measles, adding a critical commentary. Often called al-Hakim during his lifetime, Van Dyck had a large medical practice in addition to his academic duties. He resigned from the Syrian Protestant College after the 1882 commencement address by Professor