^44 ATTRACTION OF WATER BY A!R. 



motion IS generated in this experiment, which cannot be fe» 



ferred to the aftion of gravity. We muft therefore afcribe it 



to anotlier force, namely, the mutual attraction of wood and 



water in a liquid form. 



Aqueous va- Exp. 2. If a piece of whip-cord or tharm be ftretched by 



pour attiaaed by (fie heavieft weight, it can fupnort, the pendent body will af- 

 dry vegetables, , „ ° ' ^' „ ' . . " . 



gcc, ccnd, as oil as the urmg or gut contracts, in coniequeneeot an 



acceffion of water derived from the atmofphere ; on the con- 

 trary, it will defcend, when the cord begins to relax from the 

 lofs of moiflure. The motion generated in this inftance, proves 

 atmofpherical vapour to be powerfully attrad^ed by the dry 

 fibres of vegetables and animals; confequently thefe fubflances 

 have a ftrong affinity to water, not only in a liquid ibrm, but 

 alfo when it is diffufed through the air. This affinity or force 

 will be called the hygrometrical attradion in the fequel of, the 

 eflay, for the fake of perfpicuity. 

 The force of The preceding experiments have not the leafl claim to no- 



affinity perma- yelty ; but they are the preliminaries of an inference, which is 

 of moment in the prefent queftion. For affinity is a fixed re- 

 lation of bodies, creating a difpofition to coalefce, in fuch as 

 are thus mutually related, as often as water is combined with 

 another fubflance. The union mufl therefore be permanent, 

 unlefs it happens to be diffolved by an external caufe. Now 

 as any certain force only gives way to another fuperior and 

 contrary to itfelf, it is evident that a moift body, which dif- 

 charges a portion of the water it contains, is obliged to part 

 with it by a more powerful attraftion, exifiing in its neigh- 

 bourhood. It is to be remarked, that temperature is one of 

 (he external cauftis alluded to above; but it is difregarded at 

 prefent, becaufe the effects of its changes may be obviated in 

 the following experiment, which is intended to throw addi- 

 tional light upon the hygrometrical attraction. 

 Hygrometrical ^-''P' ^' Take two bibulous fubflances, fuch as two flices of 

 attradion is fponge, or a piece of fponge and flired of woollen cloth. 

 th^awSn of ^^^"^ ^^'^ ^"^ ^^' ^"^ ^^^P ^^^ other dry; then put them both 

 water. into aclofe veffel of glafs or metal, placing th6m either in con- 



tad or apart : the wet body will grow lighter in a fliort time, 

 and the dry one will gain more weight ; this procefs may be pro- 

 longed, until the two fubflances find the equilibrium of their 

 attradlive powers; which will be accompliflied, when their 

 refpc61ive weights become flationary. This equilibrium proves 



the 



