Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

APPENDIX. 309 After returning from exploring part of the river, both mountain barometers were again similarlj' compared, and the difference between the best instrument and that fixed on board was found to be the same as before, namely, 0,19 inch. At sunrise on the 5th of May, at the westernmost station reached by the boats, the mountain baro- meter which was preferred showed 29,81 (/3') ; the thermometers, attached, and detached, 44° Fahrenheit ; and the cistern of the instru- ment was one foot above the level of the river. At the same time (allowing the difference of longitude) the barometer on board the Beagle showed 30,07 (/3) ; while the attached thermometer showed 44°, and the detached 43°. The rise of tide that morning at the ship was twenty-one feet, and it was high water at thirty minutes past seven, a.m. By Baily's rule—* B = 0,00000 (subtract 0,19 from 29,81) log. H' = 1,47159 1,47159 log. H — 1,4781.3 D = 0,00654 - - - log ='7,81558 c =:'9",y9980 Half-tide 10,5 feet. A = 4,79207 — 2,5 405 = 2,60745 8 4-7 — 1 412 feet. Hence the western station appears to be about four hundred and twelve feet above the level of the eastern — that of the Beagle : but other pairs of obsen'ations were made durmg the pre\dous and following days (May 4th and 6th) of which the results, similarly deduced, were 464, 501, 527, 487, 497, 434, and 436;— each con- siderably above 400 feet : and as that part of the river (the western station) is about two hundred miles from the sea, the fall, on an average, cannot be less than two feet in each mile. » Pp. 183 and 263 of Astronomical Tables and Formul», by Francis Baily, Esq. F.R.S. Pres. A.S. &c. &c.