Art. VIII. — Remarks on some New Tables for Finding 

 Heights by the Barometer. 



By E. J. White, F.R.A.S. 



[Bead May 9, 1889.] 



Since the memorable 19th of September, 1G48, when the 

 celebrated Pascal ascended the Puy de Dome, in the French 

 Province of Auvergne, and found, as he had anticipated, 

 that the mercury in his barometer fell as he rose, the 

 barometric method of measuring heights has been extensively 

 used, and in many instances, it is the only one available. 

 Until about thirty years ago, only mercurial barometers 

 were used for this purpose. They are still the most accurate, 

 and should always be employed where the utmost precision 

 of this method of measuring is required, but they have the 

 disadvantage of being expensive, bulky, and fragile. At the 

 period mentioned above, the aneroid, which had been 

 invented in 1850 by M. Vidi, came into general use, and of 

 late years it has become so popular, that as a weather-glass, 

 or tourist's companion for measuring elevations, it has nearly 

 superseded the tube of mercury. Almost the sole reason for 

 this preference, is its portability ; good aneroids are made 

 that will go into the waistcoat pocket, while others are 

 small enough to be used as charms to be suspended from the 

 watch chain ; these latter, however, are to be considered 

 more as trinkets than as philosophical instruments. On the 

 other hand, it is not an independent instrument, but has to 

 have its scale originally marked off, and its errors from 

 time to time found, Irom comparison with the mercurial 

 barometer, than which it is also more com]:)licated and less 

 stable. 



The mathematical part of the subject has been treated by 

 many eminent writers ; but since the time of Laplace, his 

 formula has formed the basis of the investigations. If air 

 was an incompressible fluid like water, the law would be 

 very simple; the pressures would be proportional to the 



