A CGS unit of dynamic viscosity. Viscosity is a frictional property (actually, several related properties) of liquids and gases: due to friction between molecules, the liquid or gas resists flowing to a greater or lesser extent. Dynamic viscosity is measured by stating the force needed to move a standard area of one layer of the liquid or gas with respect to another layer, the two layers being parallel and separated by a standard distance filled with the same liquid or gas. If a force of one dyne is needed to move one square centimeter of the liquid or gas relative to a second layer one centimeter away at a speed of one centimeter per second, then the viscosity is one poise. The unit is named for the French physician Jean Louis Marie Poiseuille (1799-1869). Generally speaking, liquids have viscosities measured in centipoises and gases have viscosities measured in micropoises. The SI recognizes no named unit for dynamic viscosity; in SI units, one poise equals 0.1 pascal second (Pa·s). The poise is also equivalent to 14.5038 x 10^-6 reyn. P is the proper symbol for the unit, but Ps and Po are also used