222 



BOARD OF AGRICULTURE. 



dence should be placed in the barometer. After the first indica- 

 tion as above, and the barometer does not rise, but remains sta- 

 tionary, it is strong indication that the storm has not all passed. 



The foregoing rules are the result of long and careful observa- 

 tion. It must be remembered that storms occur under diflerent 

 circumstances in different parts of the globe, yet taking the first 

 three of the above rules as a basis of calculation, a short experi- 

 ence, with the exercise of the judgment, will enable one to determine 

 very correctly concerning appi'oaching changes in the weather." 



The mercurial barometer has long been used for the measurement 

 of altitudes, but the Aneroid, at once so easily and safely portable, 

 can be us^d with great facility and with such accuracy as to offer 

 the most expeditious and best method of ascertaining the elevation 

 of hills or mountains. For this purpose the starting point should 

 be the sea level, or any point above it whose hight is known. 

 The instrument should be kept as near as may be at the same tem- 

 perature, or if this is not practicable, a proper allowance should be 

 made for variations. 



If onlj' one is used, a time should be selected when the air is 

 still and not affected by disturbing causes, as a change of density 

 or of temeperature would indicate an elevation greater or less than 

 the true one. A nearer approximation to accuracy could be made 

 by using two which had been compared ; the stationary one 

 should be observed every hour, while the other is used in the 

 ascent. 



The following table of elevations has been computed, answering 

 to the corresponding depressions of the barometer.* The sea level 

 being assumed as at 30 inches, and the temperature at 55 deg. 



Manual of the Barometer, by J. H. Bellville. 



