Porpoise (scuba gear) Porpoises still exist. Only a few of these early models are known today, the rarest being the CA-2, made for use with two tanks. Porpoise (scuba gear) Porpoise is a tradename for scuba developed by Ted Eldred in Australia and made there from the late 1940s onwards. The first Porpoise was a closed circuit oxygen rebreather, and the following models were all single hose open circuit regulators. This rebreather was developed by Ted Eldred in the late 1940s and early 1950s. Some were made and used for sport diving, but they did not go into full production. It was worn
Death rates in the 20th century Death rates in the 20th century Death Rates in the 20th century is the ratio of deaths compared to the population around the world throughout the 20th century. When giving these ratios, they are most commonly expressed by number of deaths per 1,000 people per year. Many factors contribute to death rates such as cause of death, increasing the death rate, an aging population, which could increase and decrease the death rates by birth rates, and improvements in public health, decreasing the death rate. According to the CIA World Factbook, , the global crude death rate is 7.99 deaths/1,000 population.