Page 42 - My FlipBook

pounds pressure from the impulse of any stroke, or we may
mark the spaces on the register in pounds for any mallet
of given weight beforehand and read off the pounds devel-
oped in each stroke. I have a block in this instrument cut
from the same piece of wood. as that I have just been using;
they come end to end. In this experimental work I find it
necessary to be very careful as to the wood I use. That
blow is a little hard (demonstrating). It cut the paper
through. It is difficult to gauge the hand mallet accurately
in pounds, but we may determine the number of pounds in
any stroke. Now remember I was using an instrument point
so large that 45 pounds was required to penetrate the paper.
That is more force than we need to use in filling teeth. The
point is not very large, only one and one-fourth millimeters,
but is larger than we should use in filling teeth. Mallets of
different weight in producing the same impact give different
results in impulse. Now I may place the tuptodynamometer
on the falHng weight apparatus and repeat the experiment on
it, and you will find that when I drop the weight from the
same height as I did on the anvil it has not penetrated the
paper. It is just the same fall that it had before. Why that?
Not so solid. This is a very important feature and one
that we must take into careful consideration. The number
of pounds developed does not depend altogether on the
momentum of the mallet ; other features come in to modify
this. (Taking a light board and trying, while holding it in
the hand, to drive a nail.) I may drive and drive on that
nail while holding the board in my hand and not put it
through the piece of wood, but if I support the wood on the
table I drive it easily. The number of pounds developed
between the nail head and the mallet will depend upon the
conditions of resistance as well as upon the momentum of
the mallet. Now remember that in filling teeth. This anvil
of the tuptodynamometer upon which I strike is as solid, as
firm, as any tooth you will fill ; in fact, great pains was
taken in its construction to have the conditions equal, as
closely as possible, with the condition of solidity of a tooth
that is being filled. Now, in order to penetrate that paper
upon the tuptodynamometer we will have to raise the weight
nearly twice the height to get a stroke that is sufficient. The
difference between this and the absolute solidity of the heavy

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