Spread of Liquids on Solid Bodies. 329 



When the glass was replaced by a silver plate (a mirror-glass 

 silvered by Martin's process) the values were: — 



h — millim. 

 (9=12° 49' 



50 millim s. 

 6°26 / 



By A = must be understood a fall of the least possible height. 



If the drop of water is left to evaporate, or if a portion of 

 the water be removed by a clean thread of glass, the drop be- 

 comes thinner and the edge-angle smaller, the surface of con- 

 tact with the solid remaining practically unchanged. 



When with greater heights of fall the drop becomes more 

 flattened by striking upon the flat surface, the same mass of 

 fluid acquires a greater surface of contact with the solid. This 

 surface of contact retains its original dimensions, and 6 is 

 found too small. 



If fresh fluid is added to the drop, the surface of contact 

 grows more slowly than the altitude of the drop, and the edge- 

 angle acquires the same value as with minimum height of fall. 



The following measurements, when it is not expressly stated 

 otherwise, refer always to the case of minimum height of fall 

 or of maximum edge-angle. The size, and the velocity with 

 which the falling drops follow one another, have only a slight 

 influence upon the edge-angle. The deviations are at least not 

 greater than are shown by similar drops upon the most, homo- 

 geneous surface possible, and seldom amount to more than 30'. 



Accordingly I found when water was dropped from a wide 

 or a narrow siphon tube upon a freshly-cleaned black glass : — 



= 6° IV or 5° 55'. 



After the glass had laid some time in the air: — 



0=24° 7' or 25° 15'. 



A clean thread of glass was cut in two, and of it two siphons 

 bent, so that the drops formed themselves on the portions that 

 were previously united. One siphon was drawn out longer 

 and narrower at its middle point in a clean alcohol-flame so 

 that 10 drops of water formed on it during a minute, while 

 upon the other 40 drops of almost the same size were formed 

 in the same time. The edge-angle for white plate-glass then was 

 7° 30' or 6° 31', 



according to whether the drops fell slowly or quickly. 



The cleaner a surface is, other circumstances being equal, 

 the less will the edge-angle be found. 



A black glass plate cleansed with alcohol and a clean linen 

 cloth showed for water the edge-angle 



7° 34'. 



