Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.1): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

42 BAROMETRICAL OBSERVATIONS. Feb. 1827. the mercury 43°.* Unfortunately the day was very cloudy, and many squalls of sleet and rain, which obscured the hills, passed whilst I Avas taking bearings. To the N.E., towards the supposed Sebastian Channel, the horizon was too hazy to allow iTiuch view. A deep inlet was seen in that direction but whether the land closed round, or whether a channel was at the bottom, we could not distinguish. A considerable body of water was observed to the southward of Cape St. Valentyn, behind Lomas Bay, but its extent was screened from our view by the intervention of the Lomas hills. It appeared to be a channel, the opposite or eastern side of it being formed by the high ranges previously seen from Point St. Mary. Cordova's Ports San Antonio and Valdez were distinctly made out ; but, to the southward, every thing was enveloped in mist. The bearings and observations, which occupied me nearly two hours, being completed, we all adjourned to a sheltered cleft in the rock close to our station, wliere we soon recovered the use of our fingers.-|- • The result of the barometric observation for tlie height of Mount Tarn is as follows Height by one barometer ' ,^ , o'ror i [mean 2,596-H feet. ° ' l_ descent 2,b2:>-4J ' n * I r ascent 2,ni9'3\ n ma n Do. two do. I descent 2,596-7/ ~ ^^^^^'^ 2,602-2 By angular measurement from Observation Cove, Port Famine, with theodolite, allowing f\ of the intercepted arc for terrestrial refraction, the height is 2,850 feet. Another observation, with the sextant, made it 2,855 feet. The mean 2,852 I consider more correct, from the difficulty of obtaining a correct reading of the barometer on the summit. t By Daniell's hygrometer, used in this sheltered spot, I found the temperature of the air to be 48° ; dew point 41° : but upon exposing the instrument to the wind, the air M^as 39^°, and the dew point 36° : the dif- ference in the former being 7° ; and the latter 3^° ; from which the fol- lowing results are obtained air. dewpt. diff. exp. dryness. '"'to^ot^r!''''' In the ravine 48 41 7 292 776 3-323 Exposed to wind 39^ 36 3| 248 898 2-871 Difference ~8| 5 s] 44 122 0-452 The