Provenance: Formerly in the Esmond Bradley Martin collection. The watch comes from a very special series of watches finished by S. Smith for the Kew Observatory trials. The preceding lot (No. 1901-22) was the first in the series. The next watch in the series (1901-24) , a tourbillon regulator with minute-repeating, perpetual calendar and split-seconds chronograph, was submitted to the Kew Observatory trial in 1902 and obtained the highest score in the category of complicated watches. The present watch, whose serial number is between these two, is remarkable not only because of its large size, its unusual 12-hour register, but also because it has the first two-button, four-function chronograph known to exist. This system was patented in 1929 by the Swiss firm Universal Watch Co. The two-button, four-function chronograph implemented in the present watch dates from almost 30 years prior to that. In addition, it is the earliest known English flying tourbillon in existence. The patent for this type of bridgeless tourbillon was granted to Robert Benson North in 1903, No. 6737. It is reasonable to assume that this watch is the working prototype for that patent, which has been previously overlooked due to the English tendency during the late 19th and early 20th centuries, to generically describe both tourbillons and karrussel regulators as "revolving escapements". As such North?s patent was granted for "improvements to revolving escapements for watches and other portable timekeepers". It predates by 23 years the patent granted to Helwig, who is considered the father of the flying tourbillon. The finish is meticulous, with the double overcoiled balance spring that was employed in the highest qualit watches to ensure maximum isochronism. It is made of a palladium/copper alloy, which reduces acceleration, is rustproof and non-magnetic. The use of a gold escapement is the final touch in the revolving escapement?s superior finish. The watch has a six-minute flying tourbillon carriage. The carriage is built around the 3rd wheel pinion, allowing for six-minute rotation, reducing the jumping effect of the transmission. Robert Benson North (c. 1867-1929) Received his technical training at the British Horological Institute. During the course of his studies, he won many prizes for his work both theoretical and practical. In March 1898, North became Director and Manager of Nicole Nielsen and Co., Ltd., being named Managing Director in June of 1900. In 1903 he patented his "improvements in revolving escapements for watches and other portable timekeepers", No. 6737, suggesting that at the time he considered applying the tourbillon to a carriage clock. In 1905 he established North & Sons, to produce "Watford Speedometers". In October 1922 North was appointed Director and Chairman of Charles Frodsham & Co., Ltd. Robert Benson North died on March 20, 1929, at which point his son, also named Robert Benson North, was appointed Director and Chairman of the company in his father?s place. The One-Minute versus the Six-Minute Tourbillon The invention of the tourbillon defeated the inherent problem of positional error. Regardless of how well the balance is poised statically, when installed in a watch, it shows positional errors due to the sagging of the balance spring, errors caused by the centrifugal force, uneven expansion of the balance and lack of uniformity of the balance lamina. The tourbillon does not eliminate these problems, it averages them out. A tourbillon watch will not run any better than a simple one, but the period of its carriage is constant regardless of the vertical position. Consequently, although the rate of a tourbillon watch can vary within the period of its carriage, it can be regulated to be exact 1440 times within a day (in case of a one-minute tourbillon). So if a simple watch makes, say, two seconds positional error, one fitted with a tourbillon will make 0.0014 seconds per day. However, since a tourbillon is a very delicate instrument, it faces another challenge. The going train transmission of a watch moves in a jumping fashion to the rhythm of the escapement. It is stopped and re-started every fifth of a second. Furthermore, during unlocking it moves slightly backwards. The nature of the tooth-leaf friction is considerably different than in a continuously-running transmission. The ideal train is such that the output torque ? the momentum exerted on the escape wheel pinion ? is constant. Unfortunately, in standard watch type gearing, where the shape of the tooth is a modified version of the cycloidal shape, the output moment even with constant driving force, varies. This is one of the reasons it is preferable to use a six minute carriage rather than a one-minute one. It lessens the stress on the carriage caused by its constant stopping and restarting. It is interesting to point out that Breguet, the inventor of the tourbillon, used the six-minute tourbillon quite often. Thus, in general, one might say that if a watch is intended for robust use, a six-minute tourbillon is preferable, and if it is for gentle use, a one-minute tourbillon.