Bidspirit auction | AN EXTREMELY RARE OBSERVATORY TANK

AN EXTREMELY RARE OBSERVATORY TANK REGULATOR BY THOMAS MERCER, NO.500. The fine movement features Riefler's patented spring impulse escapement with double escape wheels. The rocking escapement block is made from aluminium instead of brass as in the Riefler. The movement has an electrically re-set remontoire that acts upon the 3rd wheel. The movement is bolted to a beautifully engineered and polished aluminium support that itself sits upon a steel “tank” that has a heavy blown glass dome covering it. The tank is supported by an extremely heavy and durable cast iron wall bracket that features integral levelling bolts. The Tank has a valve to allow the evacuation of air so that the pendulum swings in a partial vacuum. The clock is regulated by altering the density of the air in the tank. The regulator format dial is signed Thomas Mercer Ltd. St.Albans England. And is numbered 500 in the subsidiary 24 hour dial. - Following an objection from the Admiralty about having a German made Riefler tank regulator in the Greenwich observatory, four British firms were invited to replicate this clock. The winning submission was made by E.T.Cottingham and was duly installed at the observatory where it performed excellently. From this original clock subsequent orders were received from various observatories around the world. E.T.Cottingham were unable/reluctant to produce others so an agreement was made that the St.Albans firm of Thomas Mercer produce them. Only 5 or so were made and supplied to Tokyo, Buenos Aires and Hong Kong observatories amongst others. (138cm high)