20 ESSAYS AND OBSERVATIONS' 



in the air at fome diftanee from it, by the 

 force of a repuhive power; for, there could 

 not be any copious reflexion of white light 

 from its under furface, unlefs there v/ere a 

 real interval between it and the furface of the 

 plant*. [^^^^ Tab. iii. Fig. 2.} 



j8. If 



* Newt. Optics, query zg. 



Let AB, Tab. iii. Fig. 4. reprefent the extremity of 

 any repulfive body immerfcd in water, for inflance a flice 

 of colewort leaf, CL and DM, the convex furfaces of 

 water immediately furrounding it, and CD perpendicular 

 to AB, the common tangent of thefe curves, which 

 will be the' continuation of the general furface of the water. 

 The forces with which any two particles, E and F, are 

 prefled by the water in the diredions EG, FH perpendicular 

 to KB, are known to be as KG and KH, and the repulfive 

 powers which balance them mud be in the fame proportion. 

 If therefore the relation between the ordinate and abfcifs in 

 the curve DM could be any way found by experiment, the 

 law of the repulfive power might be determined, upon fup- 

 poiition that the particles are influenced by no force but the 

 repulfive power of the line KB and the gravity of the fuper- 

 incumbent fluid ; but their mutual attraftion, which tends to 

 leflen their lateral tendency, mull be likeways taken into the 

 account in order to an exad determination. 



Before I leave this fubjefl of attraftion and repulfion, I 

 beg leave to propofe to the Society, the fpontaneous motions 

 of light bodies on the furfaces of fluids, as a thing worthy of 

 being inquired into ; for, tho' it be manifeft in general that 

 they depend upon the difi"erent figures of the furface, it is far 

 from being an eafy matter to explain the particular cafes by 

 mechanical or hydroflatical laws. The following account: 



of 



