APPENDIX. C03IPARIS0NS OF THE ANEROID BAROMETER, 409 



g 12. Upon the journey to the north of Quito I carried mere. bar. No. 

 558 and aneroids A and B, and upon arrival at the top of the great ravine 

 of Guallabamba took simultaneous observations of the mercurial and the 

 aneroids. At the bottom of the ravine, two hours and a half later, readings 

 of all three were repeated with the following result : — 



Date. Barometer. Read at top. Read at bottom. 



Mar. 27, 1880 Merc. bar. 558 (red. to 32° Faht.) 21-692 23-929 



do. Aneroid A 21-140 23-400 



do. do. B 19-940 22-200 



The rise of the Mercurial Barometer was 2 '237 inches, 

 do. do. Aneroid A ,, 2 -200 ,, 



do. do. „ B ,, 2-260 ,, 



§ 13. The foregoing experiment is a descending one employing two ane- 

 roids, and the next is an ascending one in which three were observed. Upon 

 the occasion of the attempt to ascend Uliniza from the north, I read the 

 three aneroids A, B, D before departure from Machachi (9839 feet), and did 

 the same at our camp (15,446 feet). 



Date. 



Barometer. 



At Machachi (9 a. m.) 



At Camp (6 p. m.) 



June 8, 1880 



Merc. bar. 558 



21-176 inches 



17-222 inches. 



do. 



Aneroid A 



20-650 ,, 



16-810 „ 



do. 



do. B 



19-530 „ 



15-400 „ 



do. 



do. D 



20-290 „ 



16-380 „ 



The fall of the Mercurial Barometer was 3 954 inches. 

 The mean fall of the three aneroids was 3-960 ,, 



§ 14. Upon the second ascent of Chimborazo I carried aneroids A and E 

 to the summit, reading them at the fifth camp and at the top. Aneroid A 

 became much out of range, and I therefore cannot give its reading. 



Date. 



Barometer. 



Fifth Camp (4 a. m.) 



Summit (2 p. m.) 



July 3, 1880 



Merc. bar. 558 



16-931 inches 



14-044 inches. 



do. 



Aneroid E 



16-060 „ 



12-990 ,, 



The fall of the Mercurial Barometer was 2-887 inches, 

 do. Aneroid E ,, 3-070 ,, 



§ 15. The examples which are quoted in §§ 12, 13, 14 give the closest 

 coincidences that I can mention from amongst experiments of this order. 

 Upon the whole, it appeared to me that better values could be obtained 

 from aneroids by taking the 7nean of ascending and descending observations, ^ 

 than by taking the means of either ascending or descending ones alone, and 

 I now give an example in which this method of treatment was adopted. 



On March 19, 1880, I carried the aneroids A, B, D, E from our lodging 



^ When ascent and descent are only a short space of time apart. 



