Science facts today

* One litre human blood contains about 4,000,000,000 - 11,000,000,000 white blood cells. * Tachometer is an instrument used to measure the speed of revolution of a revolving disc or shaft. * Sloth bears are used as performing pets due to their tameable nature. * Ballistics is the branch of mechanics concerned with the study of projectiles. * More than 80% of the total described animal species of the Earth are arthropods. * Silicon is the second most abundant element in the Earth's crust (the first being Oxygen). * As gamma rays are a form of ionizing radiation, they pose severe health hazard when absorbed by living tissue. * The mass of Planet Saturn is roughly 95.152 times the mass of the Earth. * Capillary feed fountain pen was invented by Lewis Edson Waterman. * Polar bears are nearly invisible under infrared photography.