401 
the resistance experienced would be due to the weight of the stone exclusively. 
The amount of resistance, whether of weight only, or of weight and friction 
combined, depends on the gravity, and is only proportional to it, whatever the 
exertion of the horse may be. Beyond the weight and friction, there is no 
further resistance ; and this is clearly inconsistent with the dogma that 
‘ action and reaction are always equal and contrary.’ Or, again, in pressing 
the hand against a stone or other rigid substance, there is no reaction what- 
ever. According to its weight, or hardness, or strength, the substance resists. 
Beyond that, it yields or breaks. As long as the body resists the pressure, 
the resistance (». e. while the body does not yield) is certainly and therefore 
greater than the pressure. As the body does not press back, but only resists, 
the pressure is necessarily always only equal to itself ; but there is no reaction 
in this case, such as there would be if some elastic body were pressed in like 
manner.” * 
34. I must tell you, now, how some modern “ men of 
science” have written upon the same subject. In the Edin- 
burgh New Philosophical Journal , for April, 1864, Mr. Balfour 
Stewart, F.R.S. (writing anonymously), criticised my reason- 
ing, as follows : — 
“ Did Mr. Reddie ever try to open a massive iron gate, or to deliver a large 
curling-stone ? Had the weight of either body anything to do with the diffi- 
culty he experienced in handling it '? Did he ever try to stop a large grindstone 
set in rapid rotation, or was he ever struck by a cricket-ball ? We fear he 
has not been, or he would reverence the recollection of the Vis Inertice. ,} 
To this, of course, I could but answer : — 
“ That only weight in the case of the curling-stone, and weight and friction 
in the case of the ‘ massive ’ iron gate, could have to do with the difficulty of 
delivering the one, or of opening the other. And in proportion as the mas- 
siveness or weight of the stone or gate might be reduced, would the difficulty 
of moving them be lessened, till it might vanish altogether if the weight 
could vanish. The writer did not probably reflect what the word ‘ massive ’ 
really meant when making these interrogations. And I would suggest to 
him the consideration, that an empty puff-ball, almost without weight, even 
if thrown with the most frantic effort, will strike with no material force, and 
could not induce any of that ‘ reverence ’ which might doubtless follow a 
blow with something more substantial and solidly filled.” + 
35. I have, however, now to cite from a much more eminent 
Fellow and Vice-President of the Royal Society, namely, Mr. 
W. R. Grove, Q.C., who was also the President of the British 
Association at Nottingham in 1866 ; and it will, no doubt, 
* Vide Vis Inert. Vida (in Current Phys. Astr.), §§ 21 — 2C, and note. 
t Meek, of the Iicav. ( Current Phys. Astr.), note, p. 17. 
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