ON THE ATTRACTION OF SURFACES. 15 



consequent])' to apply itself to the whole surface in a very 

 thin stratum. At the instant of its fall the drop of oil dis- 

 places a volume of water equal to its momentum. But 

 presently, as the fluidity of the oil gives its particles the fa- 

 culty of gliding one upon another, the reaction of the water 

 having raised the drop, its particles, finding no obstacle, slide 

 down on all sides with rapidity, till the whole is reduced to a 

 very thin stratum. Thus in this fact there is nothing, that 

 justifies the pretended affinity of surface between oil and 

 water: on the contrary, instead of an application or reunion 

 of surface, there is rather a division and a separation; since 

 the drop of oil, which is spread upon the water, divides it- 

 self into an infinite number of others." 



With all the respect due to the talents of the professor, it This opposed 

 appears to me, that his explanation is strongly contradicted y acts * 

 by the facts on which mine is founded. I have adduced se- 

 veral experiments, in two papers inserted in the Transactions x 

 of the Italian Society of Sciences, Vols. XI and XII, which 

 show, that there is a, physical force, by which the spreading of 

 oil on water, and on other fluids, is determined. With these 

 professor Dispan could not be acquainted, otherwise he 

 would have refrained from giving his explanation of this phe- 

 nomenon. 



I would ask Mr. Dispan, how he accounts for the spread- It is not nee«*. 

 ing of oil on water, when the drop is not let fall upon it, but s , ar * r inatth f 

 - , i. , • , , • , , • . dro P should 



cautiously applied, without making the least impression upon fall, so as to 



the water, so that no reaction is produced, that can over- cause r<?act - 00 ' 

 come the affinity of aggregation of the oil. A drop so ap- 

 plied certainly spreads completely, and particularly if the 

 water expose an extensive surface. It will be still more dif- Juice of spurgs 

 ftcult for him to explain, how a drop of the milky juice of spreatswte 

 spurge, applied on water in the same manner, spreads over it 

 in the twinkling of an eye, and covers it with a very thin pel- 

 licle; or even why a small quantity of wheat flour, or any Farinaceous 

 other fecula, thrown on water, instead of falling to the bot- powders to th# 

 torn, spreads on its surface. There is no libration, no effort, 

 no reaction of the water here. It appears to me, that these 

 facts are much better explained by the principle I have esta- 

 blished 



