﻿Mr. B. Stewart on certain Experiments on Aneroid Barometers, 67 



No. of 





Correction at 













ment. 



55° F- 



72° F. 



78° F. 



88° F. 



ioo° F. 



2. 



-•105 



- #I 35 



— •140 



-•145 



-•145 



3- 



-•055 



— •090 



-•095 



-•095 



— •100 



4- 



-•095 



-■095 



-•095 



-•080 



— *o6o 



5- 



— *io6 



— •106 



— in 



— •in 



— *iii 



6. 



— 'IOI 



— in 



— •in 



— •106 



— •106 



7- 



— •061 



-•061 



— •061 



-•061 



-•031 



These results are, on the whole, very satisfactory, and appear to 

 show that a well-made compensated instrument has its indications 

 comparatively little affected by a very considerable temperature- 

 change. 



It ought always to be borne in mind that an aneroid is not capable 

 of being read to the same accuracy as a standard barometer, and that 

 the j±-q of an inch is a very small quantity. These temperature ex- 

 periments were made at the ordinary atmospheric pressure. 



I am unable to say what effect a change of temperature would 

 have at a diminished pressure. 



(3) Sudden changes of pressure. — A preliminary investigation, 

 made at the request of Mr. l)e La Rue, into the behaviour of an 

 aneroid belonging to the Italian Government, seemed to show con- 

 siderable error at low pressures. For the purpose of investigating 

 the influence of sudden changes of pressure upon the indications of 

 aneroids, I then applied to some of the best known makers of these 

 instruments, for the loan of several, and through their courtesy in 

 lending me a sufficient number, and for a sufficiently long time, I have 

 been enabled to investigate this influence at some length. 



In the following experiments the instruments were, to begin with, 

 suspended vertically, at the usual atmospheric pressure. They were 

 tapped before being read. The pressure was then lowered an inch, 

 and the instrument allowed to remain ten minutes at this pressure 

 before being read, after having again been well tapped. 



The pressure was thus reduced an inch every time, being allowed 

 to remain ten minutes at each stage ; the instrument was always well 

 tapped before being read, by means of an arrangement contrived for 

 this purpose by Mr. R. Beckley. The exhaustion was carried down- 

 wards to 1 9 inches in the case of those instruments in which the 

 scale was sufficiently great, and the instrument was allowed to remain 

 an hour and a half at its lowest pressure ; the air was then admitted 

 an inch at a time, the previous arrangement as to time and tapping 

 being followed. 



F 2 



