338 Hydrostatic*. 



cept at distances extremely small. But as a further proof, it 

 may be mentioned that all disks of the same size, whatever be 

 the substance, provided it is capable of being moistened by the 

 liquid, require precisely the same force to detach them ; so that 

 in these cases the thin lilm of water, which attaches itself to their 

 surfaces, places these surfaces and the rest of the fluid at inter- 

 vals sufficiently great to prevent any sensible action taking place ; 

 and the force required to detach all disks of the same size, what- 

 ever be the substance, is precisely the same, since it is that 

 which is necessary to detach the liquid from itself. 



455. Phenomena arising from the same cause, but differing 

 Fig 221. in appearance, are also observed when tubes of a small bore 

 are immersed in a liquid. If the liquid is of a nature to moisten 

 the tube, it will be found to ascend into the interior, and to main- 

 tain itself above the natural level. When glass tubes, for exam- 

 ple, of a fine bore are immersed endwise in water or alcohol, this 

 elevation of the fluid will take place ; and in these cases, the 

 upper extremity of the column is concave. But if the liquid is 

 not of a nature to moisten the tube, as is- the case with mercury, 

 melted lead, &c., used with glass taken in its ordinary state, the 

 liquid in the tube will be depressed instead of being elevated, 

 and the upper extremity of the column will be convex. In all 

 these cases the elevation or depression is the more considerable 

 according as the diameter of the bore is less. Such are the 

 phenomena which are called capillary from the circumstance of 

 the fineness of the bore of the tube. 



The phenomena being the same in a vacuum as in the open 

 air, they are not connected with the pressure of the atmosphere.! 



| In the discussion formerly maintained upon this subject, a per- 

 plexing fact was stated ; namely, that if a glass tube consisting of 

 two cylinders of different bores, joined endwise, be immersed in wa- 

 ter, the larger end being- downward, so as to cause the fluid to rise 

 into the smaller part of the tube, the column sustained will be of the 

 same length as in a tube whose bore is throughout of the same size 

 with this smaller. The experiment is now found not to succeed in 

 a vacuum. The peculiarity of the phenomenon, therefore, must de- 

 pend upon the pressure of the atmosphere. 



