Description and Notes:
This top quality, fully divided proportional divider is made of lacquered brass and steel and is in perfect working order. It is dated to circa 1820 as according to the Directory of British Scientific Instrument Makers 1550-1851, its maker, William Hawks Grice, was known to be working from 1818 to 1823 at 3 New Bond Street, London. This type of proportional divider was referred to as the "Bar Proportional Compass" by W. F. Stanley, and he described it in page 107 of his book, A Descriptive Treatise On Mathematical Drawing Instruments as:
Proportional compasses are very frequently made with an adjusting screw, ... This enables the slides to be set exactly to the division; it will also, by fixing the adjusting screw on a small stud provider for the purpose, adjust the points in the manner of hair dividers. This arrangement is sometimes useful, but it renders the instrument more clumsy and expensive. It can scarcely be recommended.
He then went on to recommend the French's approach of using rack and pinion mechanism to achieve micro adjustment. Stanley's comments are indeed well justified in both technical and practical aspects. However, nowadays existing examples of this type of proportional divider are very rare, and, hence, they are the most sought after ones among the collectors.