332 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 iS- 



Exper. 2. — The same thing succeeds on taking the siphon out of the water, 

 into which its lower orifice a had been immersed ; the water then falling in 

 drops out of the orifice a, and standing at last at the height ab. But in making 

 these two experiments, it is necessary that ag the difference of the legs exceed 

 PC, otherwise the water will not run either way. 



Exper. 3. — On inverting the siphon full of water, it continues without mo- 

 tion either way. 



The reason of all which will plainly appear, when we come to discover the 

 principle, by which the water is suspended in capillary tubes. 



Mr. Hawksbee's observation is as follows: " Let abfc, fig. 10, be a capillary 

 siphon, into the which the water will rise above the level to the height cp, and 

 let BA be the depth of the orifice of its longer leg below the surface of the 

 water de. Then the siphon being filled with water, if ba be not greater than 

 cp, the water will not run out at a, but will remain suspended." This seems 

 indeed very plausible at first sight. For since the column of water pc will be 

 suspended by some power within the tube, why should not the column ba, 

 being equal to, or less than the former, continue suspended by the same 

 power ? 



Exper. A. — In fact, if the orifice c be lifted up out of the water de, the 

 water in the tube will continue suspended, unless ba exceed pc. 



Exper. 5. — But when c is never so little immersed in the water, immediately 

 the water in the tube runs out in drops at the orifice a, though the length ab 

 be considerably less than the height cf. 



Mr. Hawksbee, in his book of experiments, has advanced another observa- 

 tion, viz. that the shorter leg of a capillary siphon, as abfc, must be immersed 

 in the water to the depth pc, which is equal to the height of the column, that 

 would be suspended in it, before the water will run out at the longer leg. 



Exper. 6. — From what mistake this has proceeded, I cannot imagine ; for 

 the water runs out at the longer leg, as soon as the orifice of the shorter leg 

 comes to touch the surface of the stagnant water, without being at all im- 

 mersed in it. 



I shall now inquire into the cause of the ascent and suspension of water in 

 capillary tubes. 



That this phenomenon is no way owing to the pressure of the atmosphere, 

 has been, I think sufficiently proved by Mr. Hawksbee's experiments. And 

 that the cause assigned by him, viz. the attraction of the concave surface, in 

 which the suspended liquor is contained, is likewise insufficient for producing 

 this effect, I thus demonstrate. Since, in every capillary tube, the height to 

 which the water will spontaneously ascend is reciprocally as the diameter of the 



