An unusual and rare magnetic sundial signed on the card S. Porter Fecit. March 17 1825. Entered at Stations Hall. Wooden circular case with glass dome. Velvet border. Wooden lid with expansion split. Paper label on the inside reading:
Okay, so far a simple Porter sundial….. However the compass card is made for the Far Eastern market. Chinese characters for the directions and hours. A bat motif in front of the gnomon. Never seen a Porter sundial like this before.
The invention was patented in 1824. Clever device since the user don’t need to know the position of the North in order to read the correct time….
Diameter: 54 mm.
€ SOLD Now in the collection of the Whipple Museum of the History of Science, University of Cambridge.