380 Intelligence and Miscellaneous Articles. 



perform the experiment, which he did according to my directions, 

 employing tubes having the above-assumed dimensions. I pass 

 over in silence the construction of the supports of the tubes, as 

 well as the little manipulations of the experiment : the reader who 

 has the curiosity to repeat it will find out those details for himself. 

 Now we verified that, instead of the water running away through 

 the tube c d, it reascends in this, and continues to be aspirated until 

 its free surface reaches a certain point in the slender portion, after 

 which every thing stops. Only, in order that the aspiration may 

 take place, the orifice of the tube c d must be several millimetres 

 above the liquid of the capsule ; if it is lower, the tube c d continues 

 full, the water remains suspended in it. 



A little reflection soon enabled me to understand the cause of 

 these apparently singular phenomena. The small surface which 

 terminates at a the liquid between the two tubes is concave in the 

 transverse direction ; it therefore, in virtue of its curvature, exerts 

 suction upon the whole mass of liquid to which it belongs — that is 

 to say, upon the liquid of the tube a b and that of the tube c d, the 

 latter liquid communicating with the former by the slender tube. 

 In the tube a b this suction has the effect of keeping the water 

 raised up to a' ; and it is balanced by the action of gravity, which 

 action is measured by the difference of level between the surface at 

 a' and the water of the capsule. In order that it may be in like 

 manner balanced in the tube c d, it seems at first necessary that the 

 difference of level between the surface at a and the orifice of the 

 tube c d be equal to the preceding, which would require that orifice 

 to reach the water of the capsule ; and yet we have seen that equi- 

 librium subsists even when the orifice in question is several milli- 

 metres higher. But it is because, in consequence of a tendency to 

 absorption, the water presents at this orifice a slightly concave sur- 

 face, which exerts a slight suction downwards ; and this, added to 

 the incomplete action of gravity, compensates the suction emana- 

 ting from a'. For a greater distance of the orifice from the water 

 of the capsule, the suction at a' is in excess, the liquid is drawn 

 upward in the tube cd; and this movement stops when the free 

 surface of the liquid has arrived, in the slender portion, at a point 

 where the suction due to its strong concave curvature makes equili- 

 brium with that of a'*. Such is the simple explanation of the 

 observed effects ; and this little experiment offers a curious example 

 of the suction exerted by concave liquid surfaces ; it shows us, 

 besides, an equally curious exception to the usual action of siphons. 

 — Extrait des Bulletins de VAcad. roy. de Belgique, Jan. 1882. 



* In our experiment the vertical distance from a' to the liquid of the 

 capsule was nearly 4 centim., and the least distance from the orifice of the 

 tube c d to the same liquid, for which absorption was produced, was about 

 5 millim. 



