Electromagnetic energy travels in waves and spans a broad spectrum from very long radio waves to very short gamma rays. The human eye can only detect only a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an x-ray machine uses …

Throughout history animals have accompanied men into combat as modes of transport and communication, protectors and companions. They have fulfilled a variety of roles – from carrying men and munitions to evacuating the wounded, performing guard and sentry duties to carrying out search and rescue operations, detecting gas in trenches to locating …