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I did that simply because I thought the terms I used were not open to mis- 
conception. I think the terms in which it is expressed by Newton are 
capable of some misconception ; but the drift of the law is precisely the 
same in either case. Now, if I have rightly understood him, I will just 
make a few observations in order to convince Mr. Reddie that he is making 
a distinction without a difference. Suppose I tie a string to a wall, and pull 
it with a force of twenty pounds with my hand, the wall pulls my hand 
backwards just with the same force that I pull the string from the wall ; but 
that proposition Mr. Reddie denies. (Laughter.) Well, Mr. Reddie, no 
doubt, will allow that if, instead of tying my string to the wall, I pass it over 
a pulley with the weight of twenty pounds suspended, and I pull the string, 
the weight will pull my hand back 
Mr. Reddie. — In that case, I say there would be a distinct reaction from 
the weight ; and if you ceased to pull, the weight would descend. 
Mr. Brooke. — My object is to show that the reaction is the same in either 
case. Suppose that, instead of tying the string to the wall, I attach it to a 
spring, and with a force of twenty pounds draw it from the wall. Mr. 
Reddie, I assume, would admit that it pulled my hand back ? 
Mr. Reddie. — I have noticed that kind of reaction, which is perfectly 
real. The spring acts like the weight. 
Mr. Brooke. — If I double my force of pull I shall only pull the spring out 
half the distance, and as I increase it the spring will become so strong that I 
cannot pull it out at all, until at last it becomes a part of the wall. In that 
case the reaction is just the same as in the other case ; and I would ask 
Mr. Reddie to say where he would stop. He admits that a suspended 
weight reacts upon my hand, and a spring also ; I therefore ask where the 
reaction ceases ? 
Mr. Reddie. — Wherever there is no elasticity, or pull, or spring, in the 
opposing force ; wherever you have rigidity. Take, for instance, a horse 
drawing a stone. If you brought the string over a pulley, of course the weight 
of the stone would pull back the horse, if the horse did not keep up the 
tension. There is then a distinct reaction, but you know the cause of it. 
Mr. Brooke. — As the spring becomes stronger and stronger the hand will 
be drawn out less, until at last it is not drawn out to an appreciable degree. 
Again, I will go further, and assume that I did pull the wall out — that the wall 
bends to some indefinitely small extent — a millionth part of an inch, say. I 
dare say Mr. Reddie may dispute the possibility of that, but I have no doubt 
that if one could only put a rope round the top of Eddystone lighthouse, 
and pull it out with sufficient force horizontally, one would be able to 
sensibly bend the whole lighthouse ; and when you released the rope it 
would go back again. Where, then, does the reaction cease ? 
Mr. Reddie. — It is not equal to the action. That is my point. I have 
never denied resistance in such a case ; but reaction and “ equal reaction.” 
Mr. Brooke. — But I think I have shown that it is always equal. When 
I pull the spring out, the reaction of the spring is equal to the pull I put 
upon it 
