408 COMPARISONS OF THE ANEROID BAROMETER, appendix. 



only, as the error which B had acquired was so large that we had already- 

 got beyond its range. The mean error of the aneroids at this point amounted 

 to —0-974, and their greatest difference to 1-120 inches. 



§ 9. The aneroids D and E were alone taken to the summit of Chim- 

 borazo on the first ascent, January 4, 1880, and these two were taken 

 because they were working better than the others. The readings on the 

 summit are instructive. 



Merc. bar. No. 558 . 

 Aneroid D 

 do. E . 



14-110 inches. 



13-050 



12-900 (by estimation). 



The mean of the two aneroids is seen to be 12*975 inches, and the 

 error of this upon the mercurial —.1-135 inches. I defer comment to a 

 later point. 



§ 10. Their prolonged residence upon Chimborazo seriously affected the 

 constitutions of aneroids F and G. The index of the latter instrument 

 became immovable, and the former was afflicted with a quivering action 

 which set observation at defiance. Comparisons for the remainder of the 

 journey were thus restricted to A, B, D, E only, and they are given in the 

 tables upon pp. 21-23 so far as is necessary to support the statements, — a. 

 that the aneroids acquired considerable errors ; b. that they differed amongst 

 each other to a very large extent ; and c. that their means were far from the 

 truth. 



§ 11. After we had been three to four weeks in the interior, the aneroids 

 A, B, D, E were found to hold pretty constantly together (or, speaking more 

 correctly, their movements were harmonious), and they seemed to have 

 acquired their maximum errors for the pressures at which they were used.^ 

 Of the above four instruments B had the largest index-error, and the following 

 table shows that it remained tolerably constant. It ihen became interesting 



Date. 



Place of Observation. 



Merc. bar. 558. 



Aneroid B. 



Error of B. 



Jan. 14, 1880 



Chuquipoquio 



19-683 inch 



17-820 inch 



- 1-863 inch 



Feb. 8, „ 



Hac. de la Rosario 



20-805 „ 



19-100 „ 



- 1-705 ,, 



„ 9, „ 



Illiniza (S. side) . 



17-239 ,, 



15-400 ,, 



- 1-839 „ 



,, 16, ,, 



On Cotopaxi . 



17-431 ,, 



15-650 „ 



- 1-781 „ 



. 26, „ 



Machachi . . 



21-142 „ 



19-360 ,, 



- 1-782 ,, 



Mar. 28, „ 



Hac. Guachala 



21-618 „ 



19-950 ,, 



- 1-668 ., 



May 15, ,, 



Quito .... 



21-631 „ 



19-990 „ 



- 1-641 ,, 



June 8, ,, 



Illiniza (N. side) . 



17-222 „ 



15-400 .„ 



- 1-822 „ 



to observe whether aneroids which had acquired such large index-errors 

 could be usefully employed for the determination of differences of level. 



1 See the last column of the table at p. 413. 



