THE ANEROID BAROMETER. 353 



residence, either as artisans or as agricultural settlers, 

 in Brazil. My command of the language is un- 

 fortunately so limited that I failed to extract from 

 these fellow-passengers any interesting information. 

 With scarcely an exception, each carried at least one 

 parrot, usually intended for sale at Lisbon, where it 

 appears that they are in some request Comparatively 

 high prices are given for birds that freely simulate 

 human speech. 



We were under steam in the afternoon of the 29th, 

 and soon lost to view the South American continent. 

 On the following day the barometer for the first time 

 showed the diminution of pressure which is normally 

 found in the equatorial zone. Between nine a.m. and 

 four p.m. the ship's mercurial barometer fell about a 

 quarter of an inch from 30-30 to 30'o6 inches, and my 

 aneroid showed nearly the same amount of difference. 

 It must be remembered, however, that nearly one- 

 half of the effect (at least one-tenth of an inch) must 

 be set down to the daily oscillation of the height of 

 the barometer, which so constantly occurs within the 

 tropics, the highest pressures recurring at ten a.m. and 

 ten p.m., and the lowest about four p.m. and four a.m. 



I carried with me on this journey only a single 

 aneroid barometer, an excellent instrument by Casella, 

 whose performance was very satisfactory, and which 

 in a very short time returned to its normal indication 

 after exposure to diminished pressure in the Andes ; 

 but it had the defect, which, so far as I know, is 

 common to the aneroid instruments by the best 

 makers, that the temperature at which the scale is 

 originally laid down by comparison with a standard 



2 A 



