Page:Polar Exploration - Bruce - 1911.djvu/210

206 formed round the bulb which could with difficulty be removed by scraping with a knife, or took some time to dissolve even when the thermometer was soaked in tepid water. But by changing the water in the reservoir frequently, and placing a fresh piece of muslin on about once a week, thoroughly satisfactory results were obtained, the wet bulb being further syringed daily with distilled water. The Richard hair hygrograph was employed as a check, so that any serious discrepancy between the two instruments was at once apparent. For measurement of the intensity of solar radiation a black bulb thermometer in vacuo was employed. This was fixed in a stand secured to the bridge in such a position that the sun could shine on it as nearly as possible at all hours of the day.

Two barometers of the new marine pattern were in use: one being placed in the deck laboratory at a height of seven feet above the sea, while the other was a spare instrument and was kept aft in the cabin. Three self-recording Richard barographs yielded continuous traces of barometric pressure. One of the late Dr. Black's marine rain-gauges was placed aft on the poop well clear of the deck. Its position was changed occasionally as circumstances arose, in order that it might always be on the weather side. The exposure—taking into account the various difficulties attending rainfall