158 TISCIDITY or WATER. 



other rcspocts the mobility of these particles, or rather 



of the small liquid masses composed of a great number of 



them, when they are remote from the surface and possess 



their fluidity without itnpedhnent. 



Film at the When a small solid body, placed on the surface of wa- 



of the water.* ter becomes wetted, it immediately descends beneath the 



pellicle, which no longer opposes its subsistence. At this 



period the viscidity of the water begins to manifest itself 



in a very diiierent manner, but with infinitely less efl'ect 



than when it acts at the confines of the liquid. But it is 



not yet time to enquire into this part of our subject. 



Waecr was With a view to render sensible the resistance which the 



poured on mer- peHide of the inferior surface of a stratum of viater opno- 



cury and ether *" ,. , , i , . , , , , 



upon the wa- ^es to a solid body which passes through that stratum by 



^ci"' falling freely downwards, I made the following experi- 



ment. 



EXPERIMENT VI. 



The lower sur- Having filled a small wine glass to about half its height^ 



face of the wa- with very pure mercury, I poured a stratum of water of 



mercury sup- *^*'®6 lines in thickness upon the mercury, and upon that 



ported a larger a stratum of ether of two tines. 



globule than ^vhen the whole was at rest, I took with the small 



the upper ' 



could have *ool before described a spherule of mercury of about one 



done. third of aline in diameter, and let it fall through the stra- 



tum of ether. 



This spherule being too heavy to be supported by the 

 pellicle at the superior surface of the water broke it, and 

 descended through that fluid; but upon its arrival at the 

 inferior surface it was stopped, and remained there pre- 

 serving its spherical form. 



I moved this spherule with the extremity of a feather, 

 and even compressed it ; but it always preserved its form 

 without mixing with the mass of mercury on which it ap- 

 peared to rest. 

 The lower sur- ^^ ^^^ no doubt the pellicle of the Inferior surface of the 

 Cace of gum stratum of water which prevented this contact, and as this 

 cd^jTstiinar^^'r P^^^^^^*^ ^^^ supported by the mercury on which it rested, 

 glohulc. I was not at all surprised to find that it could support 



without being broken, a spherule of mercury much larger 

 than the pellicle of the superior surface could support. 

 In order to satisfy myself that the viscidity of the water 



