332 The Rev. Patrick Keith's Reply to Mr. Meikle, [Nov. 



consequently, as being an effect of the rotatory motion. The 

 same conclusion may be deduced from premises furnished even 

 by Mr. Meikle. He maintains that the centrifugal force acts 

 directly from the centre. Be it so ; and let me ask where was 

 the force that acted directly from the centre before the com- 

 mencement of the rotatory motion ? 



After all, I am not very sure that I have caught Mr. Meikle's 

 meaning on this point ; and it may be that I have been combat- 

 ing a phantom. If so, my only fault is, my " seeming to hold 

 out that the centrifugal force acts in the direction of a tangent 

 to the orbit, and not directly from the centre." This is repre- 

 sented as a notion absurdly and peculiarly my own, and treated 

 with an attempt at merriment, as well as with an air of very 

 profound knowledge. But I think I may fairly return the com- 

 pliment, and contend that Mr. Meikle entertains notions on the 

 same subject which seem to be peculiarly ///sown. 



His first peculiarity is his establishment of what he calls the 

 well-known fact, " that the centrifugal force acts directly from 

 the centre," and not in the direction of a tangent to the orbit 

 which the moving body is describing. This he regards as being 

 established by the simple experiment of whirling a sling around 

 the head. But unless Mr. Meikle attaches some peculiar mean- 

 ing to the term centrifugal force of which I am not aware, I 

 cannot see how this experiment is any proof of the doctrine 

 which he maintains. Is it not true that a circular motion is 

 produced by the joint action of two forces ; one, that would impel 

 the body in a tangent to the orbit, if left to itself, called a centri- 

 fugal force ; and another, that would attract it to the centre, if 

 left to itself, called a centripetal force .' And is not this doctrine 

 confirmed from the phenomena of projectiles ? What will Mr. 

 Meikle say of the centrifugal force of a cannon-ball that is dis- 

 charged from the mouth of a cannon, placed either horizontally, 

 or at any angle short of 90°. At all the different elevations of 

 which it is thus capable, it has acquired a centrifugal force, and 

 yet that force is in no one case directly from the centre of the 

 earth. Does Mr. Meikle refuse to call the projectile impulse a 

 centrifugal force, or is there any other centrifugal force in the 

 case \ 



But to return to Mr. Meikle's own example. Inconsequence 

 of the intervention of the sling that connects the stone and hand, 

 and makes the latter seek the former as much as the former 

 seeks the latter (as it is said), the centrifugal force seems no 

 doubt to act directly from the centre, because the hand that 

 twirls the sling is placed in it ; though it is evident that the 

 circular motion was communicated to the stone only by the ori- 

 ginal swing that was given to the sling in the direction of the 

 first swing of a pendulum, and so carried round by the living 

 power of the hand, which, during the experiment, must have 

 been continually in action. This swing was the primary centri- 



