Humboldt State University ® Department of Chemistry

Richard A. Paselk

The CanterburyDial

in progress

My original dial was fabricated from 1/4 inch bronze (from an old plaque). The pin was turned on a watchmakers lathe from German silver round stock. The round head was then filed flat on both sides and drilled to accomodate a small silver chain. The suspension for the dial is from an old pocket watch - the dial was filed and drilled to fit this recycled part. Note the phrases stamped on the dial edges: salve factorem (save the maker) and pax possessori (peace to the possessor).

To use the dial the the month is first found and then pin is pushed from the back through the appropriate hole:

The dial is then held suspended on a string or chain and oriented so that the shadow of the pin falls within the appropriate month column. The tip of the shadow then indicates the time.

 

Making a Canterbury Dial

The The kit for this project consists of an aluminum blank (2 1/2" x 3/4" x 1/4") with three holes drilled though it for the pin and a hole in the top for the suspension ring, a small nail (1 1/8"), and a screw eye:

The screw eye is first waxed, then carefully screwed into the hole in the top pof the blank. (These screw eyes are intended for use in wood, but the soft aluminum will allow them to cut shallow threads. However, be careful not to twist too hard or the screw eye will snap off.) Next, two lines were first scribed between the holes to create three columns on each face of the dial:

Using a template set up for two simultaneous users and a dividers:

the mid-day (9 am and 3 pm) and noon marks were laid out with the dividers and then marked with a punch. The dimensions are based on a latitude of 40.54N with a pin length of 0.835" (1/4" for dial thickness + 0.585" for the gnomon). However, the actual dimensions in the Table were found following the age old tradition of copying an extant instrument - that is they were taken off the bronze dial above:

* Values are ±0.025"

Dec/Jan Feb/Nov Mar/Oct Apr/Sep May/Aug Jun/Jul
 9am/3pm 0.175 0.225 0.325 0.45 0.575 0,65
12 noon  0.25 0.40 0.675 0.875 1.325 1.675

The names of the months may then be scribed or punched to give the completed dial:

 

 


 


Instruments Medieval Science & Scientific Instruments

References

 
© R. Paselk
Last modified 23 March 2001