APPENDIX. 



309 



After returning; from exploring part of the river, both mountain 

 barometers were again similarly 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. iS' = 1,47159 



1,47159 

 log. /5 = 1,47813 



D = 0,00654 - - - log ="7,81558 

 c ='9',99980 



Half-tide 10,5 feet. A = 4,79207 



— 2,5 405 = 2,60745 



— 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 observations were made during the previous 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 Formulae, by Francis 

 Baily, Esq. F.R.S. Pres. A.S. &c. &c. 



