All through the calculus we are dealing with quantities that are grow- ing, and with rates of growth. We classify all quantities into two classes: constants and variables. Those which we regard as of fixed value, and call constants, we generally denote algebraically by letters from the be- ginning of the alphabet, such as a, b, or c; while those which we consider as capable of growing, or (as mathematicians say) of “varying,” we de- note by letters from the end of the alphabet, such as x, y, z, u, v, w, or sometimes t.

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Obviously 1 minute is a very small quantity of time compared with a whole week. Indeed, our forefathers considered it small as com- pared with an hour, and called it “one minu`te,” meaning a minute fraction—namely one sixtieth—of an hour. When they came to re- quire still smaller subdivisions of time, they divided each minute into 60 still smaller parts, which, in Queen Elizabeth’s days, they called “second minu`tes” (i.e. small quantities of the second order of minute- ness). Nowadays we call these small quantities of the second order of smallness “seconds.” But few people know why they are so called.

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What one fool can do, another can.

(Ancient Simian Proverb.)

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