466 



HYDRODYNAMICS. 



On Capillary anointed, the water rose only on the side where there was 

 Attraction no grease; that if the tube was plunged deeper than 



roh'esidn'of the P oillt to WM i cn tlle grease reached, the water rose 



Fluids, above its level ; and that a drop of water descending 



w-v^~ - on the outside of the tube was drawn into the tube 



when it was not greased, but refused to enter when OnCapillary 

 the tube was greased.* Attraction 



The following are the principal results which Carre cohesion* of 

 obtained : F1 " uids . 



Experi- 

 ments by 

 Mr Hawks- 

 bee, 17U6. 



fin glass 

 plates. 



WATER. 

 Diameter ef tube, 

 which was 12 

 inches long. 



04- of a line 



On the mo- 

 tion of a 

 drop of oil 

 of oranges 

 between 

 plass planes. 



The phenomena of capillary tubes were investigated 

 with great care by our countryman Mr Hawksbee. In 

 the year 170(5, he communicated to the Royal Society 

 an account of some experiments made at Gresham Col- 

 lege, by which it was proved that water rose to the 

 same height in capillary tubes in vacua as in the open 

 air ; and he likewise observed in bending some small 

 tubes by the flame of a candle in the manner of sy- 

 phons, that it was necessary for the orifice of the long- 

 er leg to be at least so far below the surface of stag- 

 nant water as that water in the same tube would spon- 

 taneously ascend in it, before it would run. In 1709, 

 Mr Hawksbee laid before the same learned body an 

 account of his experiments on the rise of water between 

 two plates of glass or polished marble, an experiment 

 of which he has the exclusive merit. He shewed that 

 the water rose between them whether the plates were 

 placed in vacua or in the open air ; and having found 

 that neither the figure of the vessel, nor the presence 

 of the air, nor the quantity of matter in the tubes or 

 plates, contributed to the production of the phenome- 

 na, he endeavours to explain the rise of the water, by 

 supposing the glass to act upon water in the very same 

 way as a magnet acts upon iron.t Mr Hawksbee's at- 

 tention was next directed to the motion of a drop of oil 

 of oranges between two glass planes. The drop always 

 moved towards the sides of the planes that were near- 

 est pressed together. The velocity of the drop increa- 

 sed as it approached the touching sides, and its surface 

 of course increased in a similar manner, from the great- 

 proximity of the planes. This experiment was also re- 

 peated with the same results m vacua. J Mr Hawks- 

 bee next endeavoured to measure the angle required to 

 suspend a drop of oil of oranges at certain stations, be- 

 tween two glass planes placed in the form of a wedge, 

 as shewn in our Plate CX. Fig. 6. " I procured two 

 glass planes," says Mr Hawksbee, " that measured a 

 radius of 20 inches each ; their breadth was about three 



inches ; that which I used for the lower plane was 

 placed with its surface parallel to the centre of its axis 

 and to the horizon. The planes being very clean, they 

 were rubbed with a linen cloth dipped in oil of oranges ; 

 then a drop or two of the same oil being let fall on the 

 lower plane near the axis, the other plane was laid on 

 it, and as soon as it touched the oil, the drop spread it- 

 self considerably between both their surfaces. Then 

 the upper plane being raised a little at the same end by 

 a screw, the oil immediately attracted itself into a body 

 forming a globule contiguous to both surfaces, and be- 

 gan to move toward the touching ends. When it arri- 

 ved two inches from the axis, an elevation of 15 minutes 

 at the touching ends stopped its progress, and it re- 

 mained there without motion any way. The planes 

 being let fall again, the drop moved forward till it came 

 to four inches from the centre ; then an elevation of 

 25 minutes was required to give it a fixed station. At 

 6 inches it required an angle of 35 minutes ; at 8 of 

 45 minutes; at 10 a degree. At 12 inches from the 

 axis the elevation was 1 degree 45 minutes, and so on 

 at the several stations as they stand in the annexed ta- 

 ble. This, after numerous trials, I take to be the most 

 correct, though theothers succeeded very nearly the same. 

 It is to be observed, that when the globule or drop had 

 arrived to near 17 inches on the planes from their axis, 

 it would become of an oval form ; and as it ascended 

 higher, so would its figure become more and more ob- 

 long ; and unless the drop was small on such an eleva- 

 tion of planes as was required at such a progress of the 

 drop, it would be parted, some of it descending, and 

 the rest of it running up to the top at once ; but on a 

 drop that separated these, I found the remaining part 

 of it, at 18 inches, would bear an angle of elevatian 

 equal to 22 inches, to balance its weight. Higher than 

 that I could not observe. The planes were separated 

 at their axis about ,-',. of an inch. I found but little 

 difference between small and larger drops of the oil in 



On the an. 

 gles at 

 which a 

 drop of oil 

 of oranges 

 is suspended 

 between 

 glass planes. 



See Mem. Acad. Par. 1705, p. 841, and 317, 8vo. edit. 

 t See Phil. Trans. 1707, ol. xxvi. p. L'58. 



i Id. 1711, tol. xxvii. p. 35, 



