29 2 On the Adhesion of the Particles 



distance of about one twentieth of an inch from the sur- 

 face of the water beneath ; and there, by a little inclina- 

 tion of the instrument, I caused the spherule of mercury 

 to roll gently on to the surface of the water. 



The spherule descended to that surface, and there re- 

 mained floating. 



When the eye was placed lower than the surface of 

 the water, and the spherule was observed by looking up- 

 wards through the glass, it appeared suspended in a kind 

 of bag, a little below the level of the surface. 



Having placed a second spherule of mercury on the 

 surface of the water, it immediately moved towards the 

 former, and, approaching it with an accelerated motion, 

 fell down into the same cavity, which then became lon- 

 ger ; but the two spherules did not unite. 



Having placed a third spherule on the surface of the 

 water, it joined the two others; but the weight of these 

 three spherules together being too great to be supported 

 by the kind of pellicle which is formed at the surface of 

 the water, the bag was broken, and the spherules de- 

 scended through the water to the bottom of the vessel. 



When the experiment was made with a spherule of 

 mercury a little larger, namely, about the fortieth or fif- 

 tieth of an inch, it never failed to break the pellicle of 

 the water, and to descend through that liquid to the 

 bottom of the glass. But when the viscidity of the 

 water was increased by dissolving a small quantity of 

 gum-arabic in it, still larger spherules of mercury were 

 supported at the surface of the liquid. 



A spherule of mercury of a proper size to be sup- 

 ported by water at its surface, if placed gently there, 

 would not fail to make its way through the pellicle of 

 the water, if let fall from too great an height. 



