A British Thermal Unit (Btu) is a measure of energy content, usually used to describe the energy content of fuels. Because a Btu is so small, energy is usually measured in millions of Btus. 1 Btu = the amount of energy required to increase the temperature of one pound of water (which is equivalent to one pint) by one degree Fahrenheit. This is roughly the heat produced from burning one match. 1,000 Btu = four-fifths of the energy contained in a peanut butter and jelly sandwich.
Silver Lake is a naturally formed lake of 634 acres that is over 3 km in length with a maximum depth of about 20 m. The Jones River runs for 12 km from Silver Lake to Kingston Bay with a drainage area of 77 km 2. The Jones River is the largest freshwater drainage to Cape Cod Bay. Silver Lake is included in or borders the towns of Pembroke, Kingston, Plympton, and Halifax.
The Effra is one of the subterranean rivers of London. It discharges into the Thames by Vauxhall Bridge, from which this photograph was taken. The subterranean or underground rivers of London are the tributaries of the River Thames and River Lea that were built over during the growth of the metropolis of London.