ACTION AT A DISTANCE. 



may also use a wire; but instead of pulling it, we may connect it at one end 

 with a voltaic batter}', and at tbe other with an electro-magnet, and thus ring 

 the bell by electricity. 



Here are three different ways of ringing a bell. They all agree, however, 

 in the circumstance that between the ringer and the bell there is an unbroken 

 line of communication, and that at every point of this line some physical 

 process goes on by which the action is transmitted from one end to the other. 

 The process of transmission is not instantaneous, but gradual ; so that then- is 

 an interval of time after the impulse has been given to one extremity of the 

 line of communication, during which the impulse is on its way, but has not 

 reached the other end. 



It is clear, therefore, that in many cases the action between bodies , 

 distance may be accounted for by a series of actions between each sum 

 pair of a series of bodies which occupy the intermediate space ; and it is a- 

 by the advocates of mediate action, whether, in those cases in which we ca 

 perceive the intermediate agency, it is not more philosophical to admit the 

 existence of a medium which we cannot at present perceive, than to assert 

 a body can act at a place where it is not. 



To a person ignorant of the properties of air, the transmission of force by 

 means of that invisible medium would appear as unaccountable as any 

 example of action at a distance, and yet in this case we can explain the whole 

 process, and determine the rate at which the action is passed on from one 

 portion to another of the medium. 



Why then should we not admit that the familiar mode of communicating 

 motion by pushing and pulling with our hands is the type and exemplification 

 of all action between bodies, even in cases in which we can observe nothing 

 between the bodies which appears to take part in the action ? 



Here for instance is a kind of attraction with which Professor Guthrie 

 has made us familiar. A disk is set in vibration, and is then brought m 

 light suspended body, which immediately begins to move towards the disk, as 

 if drawn towards it by an invisible cord. What is this cord ? Sir W. Thomson 

 has pointed out that in a moving fluid the pressure is least where the velocity 

 is greatest. The velocity of the vibratory motion of the air is greatest nearest 

 the disk. Hence the pressure of the air on the suspended body is less on the 

 side nearest the disk than on the opposite side, the body yields to the gn 

 pressure, and moves toward the disk. 



