PASSAGE OF WATER THROUGH CREVICES. 105 



As illustrative of the production of a continuous flow, we may cite the 

 case of a spirit-lamp, the wick of which may "be regarded as a bundle of 

 capillary tubes. If the cover of the lamp be taken off, all the spirit will 

 pass up the wick and escape by evaporation. Or in an oil-lamp, the wick 

 of which becomes readily saturated with the liquid, but never exhibits 

 any overflow, on the lamp being kindled, the oil is burned off, and a cur- 

 rent is at once established. 



I have shown that water will pass through a crevice, the width of which 

 is less than one half of the millionth of an inch. Pores or Liquids pass 

 crevices of such a dimension are invisible even with a micro- ^inut^crev 7 



SCOpe. ices or pores. 



The evidence in proof of this is very readily obtained experimentally. 

 Fig. 39. If -we take a convex lens, a, a, of 



Passage of water through a crertce. point of Contact, C, On looking down 



upon the arrangement, a black spot surrounded by a series of variously 

 colored^oireentric circles, the appearance being well known among op- 

 tical writers underlie name of Newton's colored rings. At the point 

 of apparent contact, <?, the lens and the plane are, as Newton has shown, 

 a distance apart of about the one half of the millionth of an inch, and 

 from this central point, proceeding outwardly, the distance between the 

 glasses, of course, increases. If any where at the outer portion a drop 

 of water be introduced, it extends itself instantly across all the colored 

 rings, reaching even across the central black spot. 



The three following general propositions present those phe- General propo- 

 nomena of capillary attraction which are most interesting in j^^uiyry*' 

 a physiological point of view. attraction. 



1st. If the force of attraction of the particles of a solid for those of a 

 liquid be not equal to half the cohesive force of the latter for each other, 

 the liquid will refuse to pass through a pore of that solid substance, and, 

 in a capillary tube consisting of it, will be depressed below its hydro- 

 static level. 



2d. If the force of attraction of the particles of a solid for those of a 

 liquid exceeds half the cohesive force of the latter for each other, but is 

 not equal to the whole force, the liquid will pass through a pore of that 

 solid substance, and, in a capillary tube of it, will rise above its hydro- 

 static level. 



3d. If the force of attraction of the particles of a solid for those of a 

 liquid exceeds the whole cohesive force of the latter, chemical union be- 

 tween them ensues. 



It would not be consistent with the plan of this work to offer a dem- 

 onstration of these propositions ; nevertheless, they are capable of rigor- 



