4 JOHN JOHNSTON AND L. H. ADAMS 



at one end and at the other end made fast^ to a disk, ball, or other 

 fragment of porous material; the tube is filled with water and 

 inverted in a vessel of mercury (Fig. 2). The capillary effects in 



Fig. 2. — Forms of atmometer 



the fine pores of the material are such that not only is the water 

 in the tube kept supported but, as evaporation from the surface 

 proceeds, mercury rises to take the place of the water to a height 



' By means of sealing-wax, beeswax-rosin, or in any other appropriate way. The 

 joint must of course be absolutely gas-tight. 



