BAKING A WATCH.

Hauraki Plains Gazette, Volume XXXVI, Issue 4829, 13 May 1925, Page 4

BAKING A WATCH.

A, SCIENTIFIC CUSTOM. TESTING CHRONOMETERS. Baking a watcn sounds a silly thing to do (writes J. A. Lloyd, M. 8., A.A., F.R.A.S., in the “Daily Mail”). Yet at Greenwich Observatory it is done every day. The watches arc marine chronometers. Greenwich Observatory being under the control of the Admirallty, it is pari of the routine work of that establishment to test chronometer's for the use of the Navy. This work has been continuously done there for the last hundred years.

Longitude can only be determined at sea by knowing the Greenwich time. Therefore ocean-going vessels must carry very accurate timepieces which can be relied upon to give the lime to a fraction of a second. It F for this reason that, chronometers are so rigorously tested. There are two things which must be known about a chronometer : its error, or the amount it is short of th© correct time, and its rate, or the amount it loses during 24 hours. It is the rate that is really important. When the rate is accurately known a simple correction can be added to the time shown by the dial to find exact. Greenwich time.

Il is well known that changes of temperature affect the rate ot a chronometer. Though the bala-nce-whtel is compensated against' temperature effects, the compensation can never be absolutely perfect, and oven the bast clocks in the world have a small rate. It therefore becomes necessary to determine exactly what effect any given degree of temperature may have on the going of a ship's chronometer, so that it can be allowed for at any time.

At Greenwich there are special ovens in which the chronometers ‘ire placed, and these raised to any required temperature. The l rates of the chronometers arc then compared und'?r these conditions with a standard clock. The temperature of the oven car. be maintained constant by means of thermostats, the chronometers being kept under observation by skilled men during the time of baking.

But ships often sail to high latitudes; where they meet wtih intense cold, so the chronometers must also be placed in refrigerating chambers and further tested under these conditions.

The process of wireless is fast making this work unnecestsary. Greenwich time can now be picked up a/iywhere at sea and the error of tne chro'iiometer found on.the spot. indeed, position-finding by directional wireless will in the r.ear futui'e supersede astronomical observation at sew No longer will it be necessary for the captain to “take the sun” at midday with a sextant in order to find his position.

In the comfortable seclusion of his cabin he will put on a pair of headphones and Ifeten-in for his position, which will be broadcast from powerful wireless stations in various parts of the world.