32 Oil Floating Bodies^ &c. 



to the same laws of riavit?ilon, take their direction with 

 the moviiiii; fiuid, and thus pass dijwn tie sauje incliiied 

 plane, wlih a motion mure or less ac derated as such bo- 

 dies are heavier or ligluer ; thai is, as they po^?cssa greater 

 or less power to overcome the resistance that may be op- 

 posed to thtm. 



I think it is manifest from what is here said, that ihe 

 motion which takes place with reirard to hotli duid and 

 solid, is owing- to the attraction of gravitai.on ; anl as the 

 velocities oi bodies arising fnjm this power are ijrtati'st in 

 descendino" the perj)endicular to the plane ot the honz .n, 

 90 it will follow that these velocities will be diminished un- 

 til the hue, along which they may descend, being carried 

 from the perpendicular round the whole quadrant or right 

 angle, arrives at the level or parallel to the horizon, Where, 

 if the power of d(sce.iding be toiallv opposed, or the centre 

 of gravity altogether supported, no niotion will take place. 

 Hence it will folio. v that the vt^locitv of a stream, river, or 

 current, and of course of bodies that fio.it in them, wiil be 

 i^rc-aler or less, as the inclination of the plane on which 

 ihey descend departs more or less from the line bounding 

 the horizontal plane. 



Loaded barges, beams of heavv wood, &:c., without 

 towing, and that float with the tide, will make a quicker 

 progress than the tide ; the same will take place in a river 

 or stream where there is no tide. Captain Burney having 

 asked the bargemen on the Thames the reason of this, their 

 reply was, '* That loaded barges had more hold of the tide 

 from their floating deeper than unloaded ones." This was 

 but a bad way of accounting for it ; but some reason must 

 be assigned by those who continually observed this, and 

 who Vv*ere ignorant of the real cause of it. 



The reason of this quicker progress seems to me to be 

 this: any solid floating in a fluid, and descending with it, 

 acts altogether in one mass ; and its particles thus acting 

 together conspire to overcome the resistance they meet, and 

 to divide the fluid, which, easily yielding to any pressure, 

 will make way for the body in its descent pressing forward. 

 Besides, the particles of the fluid do not act m conjunction, 

 and being easily separated thev will roll about and impede 

 each other by their friction, not only against each other, 

 but also agiiinst the sides of the river, and the bed on which 

 they descend. To this may be added, that less friction takes 

 place between the fluid and solid, as they attract each other 

 less, than between the innumerable particles of the fluid ; 

 consequently the solid will glide on^ or slip through the 



liquid 



