208 Mr POWER'S THEORY OF 



7. In order to form some sort of estimate of the forces which may 

 be expected to result from residual attractions of this kind, let us 

 suppose the fluids to be water and alcohol, and the tube to be of glass. 

 Now Gay Lussac found by experiments of great accuracy, that in a 

 tvibe of glass whose diameter was 1.29441 millimetres, water would 

 stand at the height of 23"'.3791, and alcohol of specific gravity O.8I96 

 (that of water being 1) at the height of g^^'.SgSOS. This column of 

 alcohol would be equivalent to 7™.7176 of water; the difference of 

 effects would therefore be measured by a column of water of I5"'\66l5. 

 Suppose now the diameter of the tube to be diminished a thousand 

 times, or to become 0'"'.001294, the column of water which measures 

 the difference of effects would be 1566l™'.5: or, since the French 

 millimetre = .0393708 of an English inch, a glass tube of diameter 

 0'".0000507, or about the twenty-thousandth of an inch, would produce 

 a residual effect, with water and alcohol, measured by 616.6 inches or 

 51" 4'" of water, which is equivalent to the pressure of nearly two 

 atmospheres. When it is considered that a platina wire of one three- 

 thousandth of an inch in diameter may be seen by the naked eye, it is 

 probable that the magnitude we have assigned to the capillary tube 

 is considerably greater than the diameter of the membranous pores, 

 which evade the powers of the strongest microscope. From this ex- 

 ample I think the conclusion may be fairly drawn, that, so far at least 

 as the magnitude of the force is concerned, we need be under no 

 apprehension but that the residual capillary forces are sufficient to 

 account for the sustaining force of endosmose. How far they will 

 account for the law of its variation will be seen hereafter. 



8. An attempt to explain the phenomenon by the principles of 

 capillary attraction has been already made by a distinguished mathema- 

 tician, Mons. Poisson. He first abstracts from the pressure of the 

 adjacent fluids, by supposing their altitudes above the membrane to be 

 inversely as their densities. The fluid in the tube being now equally 

 pressed on both sides, he supposes that that liquid, for which the tube 

 has the stronger attraction is drawn by this attraction to the opposite 

 end, thus filling the whole tube. The fluid within the tube, he now 

 argues, will be urged by two forces : 1st, the attraction of the liquid 



