Description and Notes:
This rare beam compass is dated to c1920 because the logo and the mark on the instrument have been identified to be used by the company in the period of 1914~1926, as indicated in this page.
The length of each of the bars is about 7.5 inches, therefore the maximum radius of the circle this compass can draw is about 21 inches. The extension bars of this compass are made of steel and are screwed together to form a rigid beam. The stability of the compass is further secured with the help of the castor. Note that W. F. Stanley has described in his book, A Descriptive Treatise On Mathematical Drawing Instruments, a tubular beam compass which can be extended or contracted like the car antenna, so it is more portable and easier to setup than this one. But he also mentioned that it is very unstable due to the flexibility of the thin tubular bars. Nevertheless I have yet to handle a real example of such beam campass in person, but a picture of which can be found in this page.