When the United States won its independence from Great Britain, it also won new lands. Soon, the Louisiana Purchase doubled the country's size. These new lands had to be explored and settled. Brave explorers, such as Lewis and Clark, soon blazed a trail to the West. How did the United States grow after the American Revolution? Why did Thomas Jefferson buy Louisiana from France? What did Lewis and Clark discover on their journey?
During the years since this book was first published in 1993 there have very few developments in the technology of magnetic particle inspection apart from improvements in instrumentation which has made the measurement of peak values of time varying currents practicable. The major changes have arisen from health and safety and environmental concerns. These involve chemicals and exposure of personnel to air-borne electromagnetic fields and long wave ultraviolet (UY.A). The changes in the acceptability of certain volatile halogenated hydrocar- bons which led to the banning of 1, 1, 1 thichloroethane in 1995 were evident in 1993. The present discussions concerning the emissions of volatile organic compounds (VOCs) in general was also current and has now reached a stage where the effects of these deliberations will become evident over the next few years. Concerns over the exposure of personnel to airborne electromagnetic fields has been current for some years as has discussions to the effects of long wave ultraviolet (UY.A) on human skin. Recommendations as to maximum permit- ted exposures over periods of time to both of these phenomena have been put forward and will doubtless form the basis of future legislation on the matter. A number of new specifications have appeared notably EN (European) and ISO specifications and some of these are still in preparation. Generally their impact will be minimal since these specifications are largely derived from existing documentation.
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