32 Mr. Meickle on Centrifugal Force, [July, 



Article V. 



On Centrifugal Force, and the Upright Growth of Vegetables. 

 By Mr. Henry Meickle. 



(To Dr. Thomson.) 



SIR, London, May 26, 1S19. 



In your number for April last, the Rev. Patrick Keith advances 

 some objections to the hypothesis of T. A. Knight, Esq. to 

 account for the direction of the radicle and germen. I do not 

 pretend to decide in favour of either side of the question, but 

 only beg to make some brief remarks on the effects of gravita- 

 tion, and on Mr. Keith's singular ideas of a centrifugal force 

 produced by rapid circular motion. Mr. Keith, in pages 253 

 and 254, seems to hold out that the centrifugal force acts in the 

 direction of a tangent to the orbit, and not directly from the 

 centre. Now this notion seems peculiarly his own, and admit- 

 ting that it were correct, some curious consequences would 

 necessarily follow. For instance, if it acted forward in the 

 direction of the tangent (as is implied in his assertion) it must 

 tend to accelerate the motion. But since centrifugal force is 

 itself the result of motion, it and the motion would mutually tend 

 to assist each other sine limite ; so that a body once set a moving 

 in a circle would not only persevere in its motion, but be accele- 

 rated ad infinitum ; and, of course, neither so much time would 

 have been wasted, nor so many brains cracked or rendered worse 

 than love-sick with the delusive and idle search after the vain 

 chimera of a perpetual motion. 



To establish the well-known fact that the centrifugal force acts 

 directly from the centre, nothing more is necessary than to attend 

 to the simple experiment of whirling a sling around the head ; or 

 indeed any weight attached to the one end of a string, while the 

 other is held in the hand, giving the weight a whirling motion, is 

 sufficient to put it past the possibility of a doubt. 



When a body is relieved from moving in a circle, its flying off 

 in a tangent is in perfect harmony with, nay a consequence of, 

 the centrifugal force's acting directly from the centre. But it 

 would be presumptuous in me to enlarge on a subject so ably 

 handled in the numerous works on the laws of motion and com- 

 position of forces. Had Sir I. Newton held any other opinion, 

 he might have had the opportunity of seeing his immortal System 

 of the Universe safely interred long before his death. 



I do not see how gravitation could have had any effect on the 

 vertical wheel at all ; for although this power is regardless of 

 motion, and acts without ceasing, yet its solicitations are not 

 instantaneously obeyed, but require time to produce any sensible 

 effect. No sooner, therefore, had gravitation desired a particle 

 to move in any one direction than it instantly itself recalled the 



