Metrication in the United States There are no U.S. customary units for electric current, potential difference, or charge since these concepts were developed after the international adoption of metric in science. The metric units ampere, volt, ohm and coulomb are the only units used. The SI term hertz has replaced the term "cycles per second" as a unit of frequency. Energy is often measured in watt hours, BTUs, therms or calories rather than the SI joule. Residential and commercial electrical energy use is metered and billed in kilowatt hours, kW·h, as in most metric countries. Force measurements regularly use the pound instead of the SI
The Civil Wars: A Tree Is Best Measured When It Is Down and a principal writer was Lebanese poet Etel Adnan, though the collage-like libretto incorporated a diverse collection of texts. Bryars set a speech by Marie Curie, "I am among those who believe that science has a great beauty", a poem by Pope Leo XIII on the then-new art of photography, and a speech by an imaginary scientist in Jules Verne's "20,000 Leagues Under the Sea". The work was not completed or publicly performed, but Bryars incorporated a number of its arias into the later works "Effarene" and "On Photography". The Civil Wars: A Tree Is Best Measured When It Is