In most churches, the decorations are red to symbolize the blood of martyrdom. Some churches remove all decorations on Good Friday, veiling anything that can’t be removed in black or purple ...

Save guides, add subjects and pick up where you left off with your BBC account. A sound wave is a vibration that travels through a solid, liquid or gas such as the air or water. A loud sound has a ...

"Written by two professors emeriti with a long and distinguished career both in research and teaching, the book clearly shows the wide experience of its authors … This is a good book, carefully ...