Emden was an avid balloonist and wrote a book on the principles of balloon navigation in 1910. He always had a practical attitude towards physics, as shown by his 1938 letter to Nature entitled "Why do we have winter heating?" Although he had retired in 1934, Jacob Robert Emden continued his scientific activities until he died in Zürich on 8 October 1940. His final paper on the temperature problems of lakes was in the press at the time of his death.