CHAPTER II. Measurements

MEASUREMENTS

§ 1. Metrology: Lord Kelvin's view of its necessity-- Its definition

§ 2. The Measure of Length: Necessity for unit-- Absolute length--History of Standard--Description of Standard Metre--Unit of wave-lengths preferable--The International Metre

§ 3. The Measure of Mass: Distinction between mass and weight--Objections to legal kilogramme and its precision--Possible improvement

§ 4. The Measure of Time: Unit of time the second--Alternative units proposed--Improvements in chronometry and invar

§ 5. The Measure of Temperature: Fundamental and derived units--Ordinary unit of temperature purely arbitrary--Absolute unit mass of H at pressure of 1 m. of Hg at 0° C.--Divergence of thermometric and thermodynamic scales--Helium thermometer for low, thermo-electric couple for high, temperatures--Lummer and Pringsheim's improvements in thermometry.

§ 6. Derived Units and Measure of Energy: Importance of erg as unit--Calorimeter usual means of determination--Photometric units.

§ 7. Measure of Physical Constants: Constant of gravitation--Discoveries of Cavendish, Vernon Boys, Eötvös, Richarz and Krigar-Menzel--Michelson's improvements on Fizeau and Foucault's experiments-- Measure of speed of light.