146 



NEQEETTI AND ZAMBBA, HOLBOEN VIADUCT, E.G., 



FIG. 



FIG. 186. 



FIG. 187. 



FIG. 



184 Sympiesometers. Previous to the invention of the Aneroid 

 Barometer, the Sympiesometer, from its extreme sensibility and con- 

 venient size, was much used for Marine observations ; but owing to 

 its liability to be put out of adjustment in transit, it is now rarely 

 used except as an instrument of comparison. Being partly acted upon 

 by the pressure and partly by the temperature of the air, its correct 

 name would be a Thermo-Barometer. 



Directions for using the Sympiesometer. It should be always 

 carried top upwards, to prevent the air mixing with the liquid. Care 

 should always be taken to screen it from the heat of the sun or cabin 

 fire. To ascertain the atmospheric pressure by the Sympiesometer, 

 note first the temperature of the mercurial thermometer; secondly, 

 adjust the pointer of the pressure scale to the same degree of temperature on the 

 scale of the air column ; thirdly, read the height of the liquid on the sliding scale, 

 the divisions and figures representing the inches and tenths of theJBarometer scale. 



Each. 



185 Sympiesometer, in wood frame, with registering index 



and plate glass front 



186 Ditto ditto, with Hackwork Movement, large size and 



best make, Oak or Rosewood Frame (fig. 186) . 



187 Pocket Sympiesometer,* suitable for travelling, and 



taking altitudes, or mountain service, in leather hinged 

 case (fig. 187) 



188 Ditto ditto, in leather case with strap for Mountain 



service . .... 



s. 



2 10 



4 10 



3 15 



440 



* The use of the Pocket Sympiesometer is now quite superseded by the Aneroid Barometer. 



