sentences:  In 1929, he became member of the Royal Netherlands Academy of Arts and Sciences.Immediately after the involvement of the Netherlands in the World War II (see Battle of the Netherlands), a friend from the United States of America, the astronomer Peter van de Kamp, offered to bring Ornstein and his family to America.However, Ornstein did not accept this offer, since, as he put it, he would not leave his laboratory in Utrecht.