# Py

**Pylon**- The tower above a bridge deck that usually carries cable stays.
**Pyramid**- In ancient Egypt, a quadrilateral masonry mass with steeply sloping sides meeting at an apex, used as a tomb.
**Pyranometer**- An instrument which measures global radiation, the combined intensity of direct solar radiation and diffuse sky radiation.
**Pyrex Glass**- A type of glass that is resistant to heat and chemical attack. Often used in cookware and in laboratory equipment.
**Pyrgeometer**- An instrument which measures the effective terrestrial radiation.
**Pyrheliometer**- An instrument which measures the intensity of direct solar radiation.
**Pyrheliometry**- The science and study of pyrheliometric measurements.
**Pyroclastic**- Fragmented rock material formed by a volcanic explosion or ejection from a volcanic vent.
**Pyroclastic Flow**- A hot, dry, fast-moving (10-100m/s) and high-density mixture of ash, pumice, rock fragments, and gas formed during explosive eruptions or from the collapse of a lava dome.
**Pyroclastic Surge**- Turbulent, low-density cloud of hot rock debris and gases that moves over the ground surface at high speed. Lower density than Pyroclastic Flow.
**Pyroelectricity**- Electric charge produced as a material undergoes a temperature change.
**Pyrolyser**- An instrument that breaks complex molecules into constituents by using heat.
**Pyrolysis**- Thermal degradation of waste in the absence of air to produce char, pyrolysis oil and syngas.
**Pyrometer**- A device for measuring the high temperatures in a furnace.
**Pyrometric Photography**- The derivation of flame temperature measurements by means of comparative photography with a calibrated light source.
**Pyron**- A unit of radiant intensity of electromagnetic radiation equal to 1 calorie per square centimeter per minute.
**Pyrophoric**- Catches fire spontaneously when exposed to air at normal room temperature.
**Pythagoras**- Greek philosopher and mathematician; held that numbers were basic to matter.
**Pythagoras Theorem**- The Square on the Hypotenuse is equal to the sum of the squares of the other two sides.
**Pythagorean Triangle**- A right triangle whose sides are integers.
**Pythagorean Triple**- An ordered set of three positive integers (a,b,c) such that a
^{2}+b^{2}=c^{2}.