On AttraBion and Refulfion. 117 



whofe weights are nearly alike j alfo water 

 tinged with cochineal at the bottom, and clear 

 water above ; and obferved that the motion in 

 thefe was at lead as great as that of the oil and 

 water. This led me to fufpedt that water alone 

 would move in the fame manner, and to make 

 the motion perceptible, I dropped into the glafs 

 Ibme powdered yellow ochre during its vibration, 

 which following the agitation of the water, ren- 

 dered it plainly vifible. The glafs was then 

 tied to a flip of wood, by which means I could 

 move it with greater velocity in the fame arc : 

 this caufed th^e waving motion to be fo ftrong 

 as to make the water roll higher on one fide of 

 the furface than the other. Laftly, a cylinder 

 of wood was fufpended by its axis in a bent wire, 

 and the vibration caufed a motion fimilar to 

 that of the fluids. 



From thefe experiments, I conclude that the 

 waving motion is produced by the difference of 

 velocity of the lower and higher parts of the 

 fluid, the higher endeavouring to return fooner 

 than the lower. The higher part of the fluid 

 may be confidered as the ball of a fliorter pendu- 

 lum than the lower, and the fluidity of the 

 water, or oil, enables its feveral parts to move 

 as freely as the cylinder of wood which rolls 

 upon its axis, becaufe the center of gravity and 

 of ofcillation do not coincide. The principle is 

 thus explained in Enfield's Inftitutes of Natural 

 1 3 Philofophy ; 



