New Forms of Stereometers. 



303 



Fig. 2. 



accompanying diagram (Fig. 3). Greater accuracy in 

 reading off the height of the mercury, and freedom from the 

 error due to capillary depression, are attained by the use of 

 two parallel tubes. The apparatus was specially designed 

 for determining the volume of a standard weight, which 

 could not be treated in the usual way. (Cf Phil. Tran.^ 

 1856, 800). 



In 1840, H. Kopp {Ann. Chein. Phainn, XXXV, 17), con- 

 structed a volumenometer (Fig. 4) in which the pressure of 

 the air is increased, instead of being decreased, as in the 

 previous instruments. The ground-glass plate (M) closing 

 the vessel (R), is held in position by a screw L and cork Q, 

 and the volume of air is then diminished by moving the 



