The Pound as a Force

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A VERY few words are necessary from me in answer to Prof. Perry's letter on page 177. First and foremost (though referring to the latter part of his letter, not to the cow and bridge portion), if any sentence in my previous communication can have led any one to imagine that I consider Prof. Perry anything but a most admirable teacher of his own subject, that sentence must have been villainously expressed. Secondly, when I said that engineers had mostly to deal in their calculations with bodies either at rest or in uniform motion, I thought I was speaking in the sense of Prof. Perry's original article (he said the same thing himself near the top of column 1, page 50), and that I should have his concurrence: I would not for a moment argue such a point with him. If I had thought it necessary to be cautious I would have used the word “suggest” instead of the word “tell” in my sentence about acceleration: to the idea in which however I still respectfully adhere. And in general I adhere to all the matter of my last communication, though with full deference to his criticism on the manner of it. Thirdly, I cannot remember that I have ever specially “advocated” the poundal. I have never much liked it, but it is useful as a stepping-stone to higher things, in a way that the familiar pound-weight is not. Fourthly, I agree with Fitzgerald that Newton's second law furnishes by no means the only measure for quantity of matter (chemical equivalence also furnishes a measure), but inertia is the fundamental property and measure for dynamical purposes. Fifthly, we do not “assume” that inertia is proportional to weight; we verify it within certain limits of error by dropping bodies (like Galileo), or (like Newton) within narrower limits by swinging pendulums: essentially the same process. Sixthly, I do not, alas, find it at all easy to give full marks to a student for his answer to such a question as “What is Ohm's law?”; and, although I cannot plead guilty to the accusation of having spoke disrespect fully either of Gravity or of Engineers, I do find that occasionally the treatment of the former by the latter leaves something to be, desired in point of clearness; the occasional educational remarks of the periodical called The Engineer, for instance, seem fairly representative of a large and influential class. And lastly, although a remark immediately following his citation of a familiar electrical equation leads me to think that Prof. Perry still misses the chief point of my letter, yet there are quantities of things in the present correspondence on which we agree; and chief among them is the profound conviction we share that there is a crying need for reform in our whole system of secondary education.

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LODGE, O. The Pound as a Force. Nature 55, 223 (1897) doi:10.1038/055223b0

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