DASYMETER. 



147 



h = difference of pressure expressed in height of water; 

 B = barometric pressure in the room ; 



t = temperature of the room ; 

 g = acceleration of gravity = 9.8088 metres. 



VOLUME BY AUTOMATIC APPARATUS. 

 DASYMETER. 



Siegert and Durr * devised an apparatus called the 

 Dasymeter, which has been introduced in several large works 

 in Europe, where it gives satisfaction. 



It consists of a balance enclosed in a cast-iron box with 

 a glass side (Fig. 36). At one end of the beam is a very 



FIG. 36. DASYMETER. 



light glass balloon holding 2 to 3 litres, sealed by fusion. 

 The other end carries a weight balancing the balloon. This 

 weight is formed of a U-tube, //, containing mercury, and is 

 open at one end; the other end is expanded into a bulb con- 

 taining air, which is submitted to the variations of pressure 

 and temperature through the mercury. If the pressure of 

 the air increases or diminishes, the mercury rises or falls, and 

 increases or diminishes the weight on the lever. Suppose an 



* Oesterreichische Zeitschrift fur B.- und H.-Wesen, xvi. p. 291. 



