84 REPORTS ON THE STATE OF SCIENCE. — 1919. 



film, one above the other, vertical slits in the metal sheaths limiting the 

 widths of the images to narrow lines. As the mercm-y pumped up and 

 down each trace upon the moving film was bounded by a wavy line 

 which represented the combined eiiect of rolling and pitching, and of 

 the vertical motion of the ship as it rose or fell upon the ocean waves 

 (fig. 3). The box was supported centrally on gimbals, dash pots being 

 provided to check the swinging. The metal stand supporting the 

 apparatus rested upon three thick felt pads to absorb as much vibration 

 as possible and the top kept in position by ropes tied to hooks on the 

 walls. In order to maintain as constant a temperature as possible the 

 experiments were conducted in the refrigerating chambers of the ships 

 upon which the voyages were made (see British Association Eeport, 

 1916), the reservoirs of the barometer being specially protected by large 

 Dewar vessels filled with cork shavings. 



Save in one respect, the whole apparatus is most beautifully constructed, 

 and it is all superbly finished, great attention being paid to making the 

 cabinet work light-tight, to the accuracy of the clockwork driving the 

 film and to the focussing and adjustment of the several images upon it. 



The general type of barometer tube favoured by Hecker has been 

 described by him in volumes entitled * Bestimmung der Schwerkraft auf 

 dem Atlantischen Ozean' (Berlin, 1903) and ' Bestimmung der Schwerkraft 

 auf dem Indischen und Grossen Ozean ' (Berlin, 1908). They possess a 

 larger space than usual above the mercury in the barometer tube to 

 diminish the effect of any residual gas, since, with a fine constriction, it 

 was not feasible to boil the mercury after it had been introduced. The 

 constriction has symmetrical, funnel-shaped entrances. Hecker claims 

 that this ensures equal resistance to the flow of mercury when rising and 

 falling, and that it possesses an advantage over the Kew marine pattern 

 in this respect. A small trap is provided to catch minute bubbles of air. 

 All barometers are engraved with short lines at equal distances apart, 

 which can be identified upon the films. 



Method of Observation. 



Before entering the small laboratory partitioned off from the main 

 refrigerating chamber, the temperature was ascertained by extracting 

 a thermometer which penetrated the wall, the door opened and closed 

 behind the observer as quickly as possible, lamps illuminating the 

 mercury surfaces switched on, heights of barometers adjusted to give the 

 images in their proper places on the films, and sheath readings noted. 

 The temperatures of all cistern and stem thermometers were recorded 

 as quickly as possible, the clockwork for driving the film started, an 

 identification mark made on the film by occulting one or other of the 

 barometer lights a certain number of times, and the room left for fifteen 

 to twenty minutes. At the end of this period aU observations were 

 repeated. A fan ran continuously in the refrigerator day and night. 

 Rubber overalls were worn in the chamber, they had some effect in 

 reducing the influence of the observer's body upon the thermometers. 

 Three sets of observations were carried out on an average each day. 



After every three or four days the exposed film was removed and 



