406 COMPARISONS OF THE ANEROID BAROMETER, appendix. 



less continued until the end of the journey ; ^ and after two months' experience 

 in the interior the behaviour of the aneroids in ascending and descending 

 was so well ascertained that one might, I think, have made use of their 

 indications to determine differences of level without committing very great 

 mistakes. 



In the following pages, I propose first to give some of my experiences, 

 and then to draw such conclusions as appear to be warranted.'- 



§ 1. Shortly before my departure from London, I made (on October 25, 

 1879) a final comparison of the aneroids against the mercurial barometer. 

 Only one of the aneroids corresponded exactly, and of the others some were 

 too high and some were too low, the greatest difference between them 

 amounting to 0*235 of an inch, and the mean of the whole showing an error 

 of + 0'148 of an inch. 



§ 2. Our ship stopped a clear day (November 20, 1879) at Jamaica, and 

 1 took the opportunity to carry the aneroids to the top of the Blue Mount- 

 ains,^ comparing them against the mercurial before starting and upon return, 

 and comparing them against each other at the highest point attained. The 

 following is the complete record, and it will be seen from it that the mean 



No. of Barometer. 



At start. 



At top. 



On return. 



Aneroid 580 



29-980 



25-430 



29-975 



A 









29-850 



25-500 



29-850 





B 









29-800 



25-250 



29-800 





c 









29-700 



25-120 



29-650 





D 









39-850 



25-400 



29-880 





E 









29-800 



25-300 



29 750 





F 









29-750 



25-350 



29-700 





G 









29-800 



25-310 



29 700 



Extreme differences 



0-280 



0-380 



0-325 



Mean of aneroids . 



29-816 



25-332 



29-788 



Merc. bar. No. 554 . 



29-876 



. . . 



29-854 



Mean error of aneroids 



- 060 





- 066 



error of the aneroids (which in London was + 0-148) had changed on arrival 

 at Kingston to — 0-060, and upon return in the evening of November 20 

 it was still further increased to — 0-066. 



J In all the comparisons which are made throughout this paper the readings of the 

 mercurial barometer are reduced to 32° Fahf;. 



2 Paragraphs 1-10 should be read in connection with the tables at pp. 412, 413. 



3 Drove to Gordonstown, walked thence to Newcastle, and on until we came to a 

 notch in the mountains commanding a view of the northern side of the island. Read the 

 aneroids at this place. 



