\6 ON THE ATTRACTION OF SURFACfS. 



blished in the two papers abovementioned, than by the mecha- 

 nical operation imagined by Mr. Dwp&n. 

 The oil collect- J | inow wt \\ f t h Ht ^ ( j rop f vl [ breaks, after it has spread 



vain into i i • n • 



drops no aigu- upon the water, and that it collects into other very small 



jueut. drops: but this dens not hinder the spreading of the oil 



from being occasioned by a force, which has compelled it 

 to diffuse itself over the surface, and before acted for a 

 moment. 



Thatasubse- But it is not true, that, if, after the spreading of the first 



CT'et tlr ° P ' a stJCon( * ancl a tnirci l)e a ppl' ,e( l to the surface of the 



•piead, not ow- water, they do not spread like the first, because they find an 

 Stance tfthe oi)StacIe t() their movement, and to their gliding on the water, 

 former, since it in the fragments of the drop of oil, which was before spread, 

 pm freeft-oin am ' occl, P' ec ' Ml surface: for the phenomenon does not take 

 •il. place, though the drops be applied far from the space occu- 



pied by the diffusion of the first drop; and though the eye, 

 assisted by a lens, have previously ascertained, that the sur- 

 face of the water is free from every obstacle in the place 

 to which the drop of oil is afterward applied. 

 Oil no obstacle I could prove to him likewise, that these obstacles are not 



to the spread sufficient to prevent the diffusion of fluids and other substan- 



of the juice of r , .. / 



spurge, which ces » that spread on water. Let a drop or oil spread over the 



impels it in a sur f ace f some water in a goblet, and when it has completely 

 globule lo one & . . ,f. 



*ide$ covered it, apply a drop of the juice of spurge; this fluid will 



diffuse itself over the surface with astonishing rapidity, though 



' the surface is already occupied by the oil spread on it before, 



and, displacing the oil, will force it to accumulate in-one or 



two drops against the side of the glass. It will be just the' 



•rof flour, same, if, instead of the juice of spurge, a little flour be ap- 



which collects pjj^j to the water; for this will equally spread over the sur- 



tbe 01! in a glo- l , , , .,-?,,,,. • 



bule under it. wee ot the water, and the oil will be obliged to unite into a 



single drop or globule, which will sink under the flour, that 

 occupies the surface. What other reason for these pheno- 

 mena can there be, than the force of adhesion between the 

 surface of the water 'and these substances? 

 Adhesion has Lastly I have to observe, that I never asserted there was 

 some proper- any thing of chemical action in this phenomenon. I only 

 mon withche- saiu " m m > ^ rst P a per on the attraction of surfaces, Vol. XI of 

 aiical affimity. t | ie Italian Transactions, that the force which natural philo- 

 sophers 



