THE SURFACE TENSION OF LIQUIDS. 591 



THE SURFACE TENSION OF LIQUIDS. 



Bt w. h. laeeabee. 



w 



HAT is it that keeps a drop of water in shape ; that enables 

 it to resist a considerable pressure or blow before it will 

 collapse into a spatter ; that holds it in its integrity to a leaf or 

 the eaves till it is mature to fall, while it still maintains its 

 round, independent individuality ? Whatever the power is, it 

 appears yet more distinctly in a globule of mercury, which will 

 not be hammered out of shape or compelled to spread. Dr. 

 Thomas Young conceived, for the explanation of this and some 

 other phenomena exhibited by small, isolated liquid masses, the 

 idea of their being surrounded by a thin, elastic membrane, less 

 dense than the deeper parts of the drop, and capable of adhering 

 perfectly to them, and more or less strongly to solid bodies. It 

 seemed capable of opposing a certain resistance to being rent, and 

 this was called its superficial tension. Some' curious movements 

 take place when certain solid substances are cast upon water, to 

 account for which Dutrochet supposed a new force, which he 

 called epipolic force. These phenomena of the drops, the " epipolic 

 force/' the calming effects of oil on storm-disturbed water, and a 

 variety of other curious actions hitherto unaccounted for, have 

 lately been referred to this property of superficial tension. Tak- 

 ing a drop of water as typically embodying the property, M. E. 

 Gossart * asserts that all the energies of nature may be found in 

 its tenuous envelope. Besides M. Gossart, studies of the curious 

 and protean properties of this superficial tension, or the envelope 

 of the water-drop, have been published by M. H. Devaux f and M. 

 Van der Mensbrugghe. J The present article is a summary of some 

 of the results of their studies. Regarding water in a vessel, M. Van 

 der Mensbrugghe finds that whatever may once have been thought 

 on the subject, it is not equally constituted throughout. Its parti- 

 cles are solicited by attractive forces which are exhibited when, 

 upon drawing out a pencil which has been dipped into the mass, 

 a drop is found adhering to the point. If this drop be conceived 

 to be cut by a horizontal plane, all the parts below the plane 

 may be supposed to be sustained by those which are above it. 

 It is also acted upon by repulsive forces tending to scatter the 

 particles, the effects of which are seen in evaporation. "When the 



* " A Voyage on the Surface of a Drop of Water." Lecture before the Scientific and 

 Literary Society of Caen, published in the "Revue Scientifique," 1887. 



f " Spontaneous Movements of certain Bodies on the Surface of some Liquids," " La 

 Nature," 1888. 



\ " Superficial Tension." Lecture before the Belgian Society of Microscopy, March 3, 

 1888, published in "La Nature," 1888. 



