Mr. Nixon's Theory of the Spirit-Level. 357 



held with the lower end rather more than O-l inch above the 

 water, the air entered also at that depressed end, and in ef- 

 fecting a junction with the air previously introduced at the 

 upper orifice, burst a film or thin plane of water extended 

 across the tube almost close to the depressed end. (13). This 

 film (which would abruptly form again, and in the same place 

 on lowering the tube) was ruptured, on taking the tube hori- 

 zontally out of the water, at the middle of the length of the 

 tube. (14). When completely out of the water, a portion of 

 that fluid remained at the bottom of the horizontal tube at a 

 depth of about O'l inch. (15). One end of a tube, having 

 a bore capable of raising water half an inch above its level, 

 being hermetically closed, a disk of thin paper covering the 

 other orifice was secured to the tube by means of melted wax. 

 This end (purposely left rather moist within) being placed 

 vertically in water at a considerable depth, the wax and paper 

 were forced completely off; yet the water, from the resistance 

 of the included air, did not rise more then O'l inch within the 

 tube. (16.) Repeating the experiment with the half-inch tube, 

 the water stood within it about the preceding height; but in 

 bringing the tube nearly horizontal, the included air protruded 

 a little beyond the upper part of the orifice, continuing to 

 escape gradually in small bubbles. (17.) When the tube, 

 wholly immersed in the water, appeared to be exactly hori- 

 zontal, the residue of the air, in figure like the bubble of a 

 level, reached within O'l inch of each end, and did not at- 

 tempt to escape until the stoppered end was slightly depressed, 

 when the whole rushed abruptly out. But when the tube, in 

 a subsequent experiment, contained only a small quantity of 

 air, so that the (more spherical) bubble was at a considerable 

 distance from each end, the stoppered end was obliged to be 

 depressed several degrees, before the bubble could complete 

 its escape. 



On a careful review of the experiments, will not a diminished 

 specific gravity of the water immediately in contact with the 

 glass, together with the cohesion of its particles, account for 

 every observed violation of hydrostatics ? In a narrow tube 

 the particles of water within it may be considered as equally 

 acted upon by the maximum of the force peculiar to the sur- 

 face of the glass which tends to diminish their specific gravity ; 

 whereas the particles within a wide tube are mostly at some 

 distance from that force, especially where it is greatest, and 

 are also influenced in a contrary sense by the cohesion of a 

 greater number of particles beyond the eliect of the force in 

 question. Hence the same external pressure causes the lighter 

 water within the small tube to rise higlicr than the heavier 



water 



