CAPILLARY ATTRACTION DESCRIBED. 25 



ally supposed. The action in the leaf and the action in the spongiole is the same, and 

 it is precisely an example of what takes place in the passage of arterial blood to the 

 veins in the systemic circulation of the mammalia. 



68. It is not worth while to expend any space here in refuting the old explanations 

 of these different circulatory movements, nor in detailing how, in the opinion of some 

 physiologists, even in the most rigid vegetable stems, the juices are propelled by alter- 

 nate dilatations and contractions of the woody tubes, much in the same manner as mo- 

 tions are executed by the dorsal vessels of certain animals. Nor need we describe how 

 the vital principle that chimera of the Dark Ages, which has kept physiology in the 

 rear of all other sciences can be brought to give one of its usual, and expeditious, and 

 unsatisfactory accounts of the phenomenon. 



69. Without wasting time, therefore, on those futile explanations, let us pass at once 

 to the philosophical principles which are involved, and show how the doctrines of 

 common CAPILLARY ATTRACTION are capable of giving not only a comprehensive, but 

 also a beautifully simple explanation of the whole phenomena, no matter whether they 

 are found in flowering or in flowerless plants, in sponges, or in the mammalia. 



70. CAPILLARY ATTRACTION, of the physical cause of which I shall presently speak, 

 takes its name from the circumstance, that if a glass tube of small diameter, or even as 

 fine as a hair (capillus), be immersed at one end in water, the water immediately 

 rises above its true hydrostatic level to an altitude which is greater in proportion as the 

 tube is smaller ; in tubes of very narrow diameter, such as those here referred to, an 

 elevation of many inches is without any kind of difficulty obtained. Thus, mjig. 108, 

 if some water be placed in a cup or other vessel to the height A B, and there be plun- 

 ged into this water glass tubes such as D, E, the water at once spontaneously rises 

 in those tubes to a height which is greater in proportion as the tube is narrower. In 

 E, therefore, it rises higher than in D. 



71. But this elevation from the true hydrostatic level only take place with certain 

 liquids in certain tubes. Thus, with the same glass tubes, D and E, if quicksilver is 

 used instead of water, so far from there being an elevation, there is an analogous de- 

 pression. The liquid metal is forced down, as it were, beneath its proper level to a 

 greater depth in proportion as the tube is narrower. And that this depends on the 

 chemical relation which subsists between the liquid employed and the substance of 

 which the tube consists, is clearly shown by smearing the interior of a glass tube with 

 tallow or oil, and then immersing its end in water. The water, under these circum- 

 stances, so far from rising, is, like quicksilver, depressed. 



72. The physical law under which these elevations and depressions takes place is 

 very simple, and important to be remembered. If a liquid can wet the surface of a 

 solid, it will rise in a tube formed of that substance ; but if a liquid cannot wet a solid, 

 it will be depressed below its true level in a tube formed of that substance. 



73. Suppose, now, we had a glass tube immersed in water, a tube of such diameter 

 that it could cause the water to rise to the altitude of twelve inches, and the tube be 

 broken off so that it is only six inches long. The theory of capillary attraction, and 

 also direct experiment, show that under these circumstances the water will rise to the 



D 



