As noted earlier Kristian Birkeland, reporting in 1903 on his expeditions to the auroral zone, proposed that magnetic disturbances accompanying the aurora were caused by large electric currents flowing down the length of auroral formations. ... Some scientists disagreed with Birkeland and claimed the electrojets did not connect to space but instead their entire circuit lay inside the ionosphere, like that of other ionospheric currents known at the time, believed to be caused by atmospheric tides. ...

... a) As source material for the high-school or college curriculum, especially in physics. astronomy and their history. (b) As a source of supplemental projects by high school students or by undergraduates. (c) As material for independent studies, In particular by motivated students who seek to know more about space . ... Those wishing to look up specific topics are advised to use the index file, accessible from the end of any "Exploration" file. ... files not listed and at other resource material. ...