45 



cause of the variation is satisfactorily established, and 

 its exact amount for every degree of temperature accu- 

 rately determined; whereas in the former case the 

 cause requires further explanation. Of how little im- 

 portance this explanation is for the popular use of the 

 Aneroid, the following observations will show. 

 Simultaneous observations of the Aneroid and Mercurial 

 Barometer for the month of March 1848. 



