146 



WELLS'S NATURAL PHILOSOPHY. 



Pig. 139. 



An immense weight suspended by a dry rope, may be raised a little way, 

 by merely wetting the rope; the moisture imbibed by capillary attraction mto 

 the substance of the rope causes it to swell laterally and become shorter. 



Capillary attraction is also iustrumeutal in supplying trees and plants with 

 moisture through the agency of the roots and underground fibers. 



What are the ^^2. The terms ExosMOSE and Endosmose 

 Exosn^srand ^'^6 applied to tliosG currents in contrary direc- 

 Endosmose? tions wbich arc established between two liquids 

 of a different nature, when they are separated from each 

 other by a partition composed of a membrane, or any porous 

 eubstance. 



The name Endosmose, derived from a 

 Greek word, signifies going in, and is ap- 

 plied to the stronger current; while the 

 name Exosmose, signifying going out, is 

 applied to the weaker current. 



The phenomena of Endosmose and Ex- 

 osmose, which are undoubtedly dependent 

 on capillary attraction, may be illustrated 

 by the following simple experiment : — If 

 we take a small bladder, or any other mem- 

 branous substance, and having fastened it 

 on a tube open at both ends, as is repre- 

 sented in Fig. 139, fill the bladder with 

 alcohol, and immerse it, connected with 

 the tube, in a basin of water, to such an 

 extent that the top of the bladder filled 

 with alcohol corresponds with the level 

 of the water in the vessel, in a sliort 

 time it will be observed, that the liquid 

 is rising in the tube connected with 

 the bladder, and will ultimately reach the 

 top and flow over. This' rising of the al- 

 cohol in the tube is evidently due to tho 

 circumstance that the water permeates 

 through the bladder, with a certain de- 

 gree of force, producing the phenomena 

 which we call endosmose, "going in;" the eflect being to elevate the alcohol to 

 a considerable height in the tube. At the same time, a certain quantity of 

 the alcohol has passed out through the pores of the bladder, and mixed with tho 

 water in the external vessel. This outward passage of the alcohol we call 

 exosmose, '' going out." A less quantity of the alcohol will pass out of the 

 bladder in a given time to mingle with the water, than of the water will pasg 

 in, and consequently the bladder containing the alcohol having more liquid 

 in it than at first, becomes strained, and presses the liquid up in the tube. 



