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Difference engines are strictly calculators. They crunch numbers the only way they know how - by repeated addition according to the method of finite differences. They cannot be used for general arithmetical calculation. The Analytical Engine is much more than a calculator and marks the progression from the mechanized arithmetic of calculation to fully-fledged general-purpose computation.

Physical Legacy Aside from a few partially complete mechanical assemblies and test models of small working sections, none of Babbage's designs was physically realized in its entirety in his lifetime. The major assembly he did complete was one-seventh of Difference Engine No. 1, a demonstration piece consisting of about 2,000 parts assembled in 1832. This works impeccably to this day and is the first successful automatic calculating device to embody mathematical rule in mechanism. A small experimental piece of the Analytical Engine was under construction at the time of Babbage's death in 1871. Many of the small experimental assemblies survived, as does a comprehensive archive of his drawings and notebooks. The designs for Babbage's vast mechanical computing engines rank as one of the startling intellectual achievements of the 19th century. It is only in recent decades that his work has been studied in detail and that the extent of what he accomplished becomes increasingly evident.

Ice was harvested and stored in China before the first millennium. Hebrews, Greeks, and Romans placed large amounts of snow into storage pits and covered this cooling agent with insulating material.

By the late 1950s, officials of the Eisenhower administration, after having seen the results of numerous atomic bomb tests, had a fairly realistic idea of how difficult it would be to survive a nuclear bomb blast. They continued, however, to disseminate somewhat dubious survival information, primarily to give the American public a sense of hope and control over their own lives. They also believed that a public confident of surviving an atomic war would support the federal government's decision to increase its own atomic arsenal, even though its existence could provoke a nuclear war with the Soviet Union.

Today, the world is attempting to control nuclear proliferation through diplomacy and treaties. In 1996, the Comprehensive Test Ban Treaty prohibited nations from using bombs for either military or research purposes. Forty-one states with nuclear capabilities have signed the treaty, but it cannot take effect until three more nations join. India, Pakistan, and North Korea are among the countries that have refused. Although the United States has signed the treaty, it has not ratified it yet.

The Manhattan Project was the code name for the U.S. effort during World War II to produce the atomic bomb. The program was under the leadership of Gen. Leslie Groves, and theoretical physicist J. Robert Oppenheimer. The main laboratory was built on an isolated mesa at Los Alamos, New Mexico. The first atomic bomb was tested at Alamogordo, New Mexico, on July 16, 1945.

scientists unraveled the structure of the atom, revealing the electron and proton. 

in 1938 fission of uranium atoms by neutrons was carried out in Germany. The energy associated with fission opened the possibility for powerful weapons and also the production of energy for civilian use.

The United Nations attempted to develop a policy for control of nuclear weapons, but the United States and the Soviet Union could not agree. This was but one component of the emerging Cold War between the two nations. Citizens of all nations saw the power of nuclear fission as massive threat as well as a source of useful energy for mankind.