This E-book contains a useful introduction to Scuba Diving for those considering the sport.
 
The Ocean - Our Most Unexplored Frontier
Many people think that space is our final frontier - and that is not entirely true. While it is more difficult to get to outer space, we probably know more about the various planets and environments in space than we do about what lies beneath the surface of our oceans.
Just as in outer space, there is a whole environment, or ecosystem, under the waters that cover 75% of our planet, with 70% of our planet being ocean waters. Beneath those waters there really is an entirely new world -a world full of beauty and mystery that few humans have the opportunity to experience.
But the lucky few who do have the opportunity to experience this vast under water world are able to do so because they are scuba divers. Obviously, human beings cannot breathe underwater, so instead, they rely on a portable respiratory system that is self contained.
In fact, that is what the word Scuba means: Self Contained Underwater Breathing Apparatus. This apparatus allows human beings to dive to depths that were once unthinkable, and to stay under the water for long periods of time, depending on how full the air tank is. Different mixtures of