426 Rev. J. B. Emmet t on the [June, 



entirely superficial is evident : take a thick tube, having the 

 same opening, and the water will rise no higher. 



A steel wire of 1-lOth inch in diameter will lift a weight of 

 several hundred pounds without breaking ; therefore the attrac- 

 tion between two circular discs of steel of l-lOth inch in diame- 

 ter exceeds by many million times the weight of a disc, having 

 the same diameter, and a thickness equal to the diameter of one 

 particle of steel ; yet the attraction of two large masses of steel 

 IS almost insensible, if there be any sensible distance between 

 them. These have been supposed to arise from a force which 

 varies inversely as the cube or fourth power of the distance ; 

 such a force does not exist, as will appear from the following 

 reasoning, which depends upon four phenomena. 



Phenomenon 1. Place together the surfaces of two perfectly 

 plain plates of glass; on separating them, their mutual attraction 

 will be very sensible, even if a single fibre of silk be interposed ; 

 it acts in vacuo, or in the air. 



2. A drop of any liquid will adhere to the under surface of a 

 horizontal plate of glass or metal. 



3. Two drops of any liquid, as mercury, water. Sec. placed 

 upon a horizontal plate of glass or metal, and very near to each 

 other, approach and unite into one drop. 



4. When two gases which do not combine chemically, as car- 

 bonic acid and hydrogen, are placed in a vessel in the order of 

 their specific gravities, they soon attain a state of perfectly equa- 

 ble mixture. 



From phenomenon 1, solids exert upon each other a sensible 

 force of attraction, when their surfaces are placed in contact 

 with each other, which vanishes when the distance becomes sen- 

 sible. Since all liquids expand by heat, and contract by cold, 

 and since the quantity of the expansion is sensible compared 

 with the entire volume, the particles of any liquid cannot touch 

 each other at the ordinary temperature of the air, but are at a 

 distance which bears a finite ratio to their diameters : at that 

 distance, phenomena 2 and 3, their mutual attraction very 

 greatly exceeds their weight, and from 3 is sensible at measura- 

 ble distances. 



From phenomenon 4, the mutual tendency of gaseous particles 

 to each other exceeds their weight at a distance which is many 

 times greater than their diameter. 



Suppose these effects to result from a 

 force which is inversely as the cube of 

 the distance. Take an evanescent or 

 elementary pyramid CAD, whose ver- 

 tex is A ; let a corpuscle be placed at A ; 

 take two sections K L, G H, parallel to 

 each other ; and let these sections be 

 evanescent plates of matter of equal 



