CHAPTER II.
MEASUREMENTS Sec.1.

METROLOGY Not so very long ago, the scholar was often content with qualitative observations.

Many phenomena were studied without much trouble being taken to obtain actual measurements.

But it is now becoming more and more understood that to establish the relations which exist between physical magnitudes, and to represent the variations of these magnitudes by functions which allow us to use the power of mathematical analysis, it is most necessary to express each magnitude by a definite number.
Under these conditions alone can a magnitude be considered as effectively known.

"I often say," Lord Kelvin has said, "that if you can measure that of which you are speaking and express it by a number you know something of your subject; but if you cannot measure it nor express it by a number, your knowledge is of a sorry kind and hardly satisfactory.