424 OF CAPILLARY ATTRACTION AND THE COHESION OF FLUIDS. 



plate, have no influence whatever upon the fluid with which it is 

 brought in contact ; whence it follows, that the indefinitely thin lamina 

 of fluid which attaches to the surface of the plate, interposes between 

 it and the rest of the fluid in the vessel, a sufficient distance to prevent 

 any sensible effect from their mutual attraction ; and furthermore, it 

 appears that the force which is requisite to detach all the equal laminae 

 of the fluid is the same, being that which is required to separate an 

 individual film of the fluid from the rest. 



Again, it is manifest from observation, that water of the same tem- 

 perature, rises to the same height in capillary tubes of the same bore, 

 whatever may be the thickness of the glass of which they are con- 

 stituted; from this we infer, that the laminse of the glass tube, 

 however small their distance from the interior surface, have no 

 influence in promoting the ascent of the fluid. 



If the inner surface of a capillary tube be covered with a very thin 

 coating of tallow, or some other unctuous substance, the water will 

 not ascend, for in that case the capillary attraction is destroyed ; 

 hence we conclude, that the action of gravity and capillary action are 

 different in their nature, for if they were similar, the capillary force, 

 like the force of gravity, would act through media of all kinds, and 

 consequently, would cause the fluid to rise in the tube, notwithstand- 

 ing its inner surface being coated with grease. 



531 . From the preceding experiments, and others of a kindred charac- 

 ter, it is inferred, that the force of attraction in a capillary tube, when it 

 exceeds the mutual attraction of the fluid particles, extends its influence 

 no farther than to the fluid immediately in contact with it, which it 

 raises; and the water thus raised, by forming an interior tube, in virtue 

 of its own attraction, raises that which is immediately in contact with 

 itself, and this again, by extending its influence to the lower particles, 

 continues the operation to the axis of the tube. 



The direction of the first elements of the fluid, depends entirely 

 upon the respective natures of the fluid, and the solid with which it 

 comes in contact ; if these are the same in all cases, the direction is 

 invariable, whatever may be the form of the attracting surface, whether 

 it be fashioned into a tube, or retains the simple form of a plane ; but 

 the direction of the other elements, or those which are situated out of 

 the sphere of sensible activity of the attracting surface, depends solely 

 on the mutual effect of the fluid particles, and the form which the 

 surface of the fluid assumes, is also regulated by the same cause. 



532. From numerous experiments and careful micrometrical observa- 

 tions^ has been ascertained, that when water moves freely in a capillary 



