Hydrogen fills the interstellar medium of our Galaxy. While some of this hydrogen is hot, and completely ionized, radio observations at a wavelength of 21~cm find a sky filled with signals from cold ,neutral hydrogen. This Small Grant for Exploratory Research award will allow Dr. Verschuur to observe interstellar neutral hydrogen at high spatial resolution. Using the Zeeman effect, he will easure the magnetic fields in regions of enhanced 21~cm emission. He expects to see the magnetic field reverse sign in a manner consistent with the idea that the emission derives from a ``tube" of hydrogen that has coupled to a strong magnetic field. Dr. Verschuur understands the problems with interpreting a signal projected from a three-dimensional volume onto a two-dimensional surface. He feels that the signals that have led to a description of interstellar hydrogen as ``clouds," suggesting a roundish, 3-dimensional structure, have been incorrectly interpreted and that these signals instead originate from a linear structure twisting in the magnetic field of the Galaxy. These observations will, first, provide more values for the magnetic field strength and its variation in the Galaxy. Most importantly, they will lead to an improved understanding of the morphology of hydrogen in the interstellar medium.
