DescriptionWestinghouse Van de Graaff atom smasher - cutaway.png
English: Cutaway drawing of the Westinghouse Atom Smasher, a Van de Graaff generator built in 1937 at the Westinghouse Corporation research center at Forest Hills, Pennsylvania, USA. It consists of a Van de Graaff generator which generates 5 million volts (MV) on its dome shaped electrode, which is used to accelerate charged subatomic particles through an evacuated tube parallel to the generator's charge carrying belt. Since open-air Van de Graaff machines are limited to about 1 MV by leakage of current from its electrode by arcs and corona discharge, the machine is enclosed in an onion-shaped air tank pressurized to a pressure of 120 pounds per square inch, which allows it to reach a voltage of 5 MV.
This 1937 issue of Popular Science magazine would have the copyright renewed in 1965. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. Search of the Renewals for Periodicals for 1964, 1965, and 1966 show no renewal entries for Popular Science. Therefore the copyright was not renewed and it is in the public domain.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.