This thesis document was issued under the authority of another institution, not NPS. At the time it was written, a copy was added to the NPS Library collection for reasons not now known. It has been included in the digital archive for its historical value to NPS. Not believed to be a CIVINS (Civilian Institutions) title.The object of this thesis is an examination of the validity of geostrophic calculations of the downstream component of the time averaged Florida Current in the Straits of Florida by comparison of calculated and directly measured current fields. The study is motivated by the assumption made in modern inertial current theory that downstream current speed is in geostrophic balance, plus evidence of recent studies indicating that this region of the Florida Current is primarily inertial in nature. The principal conclusion reached is that geostrophic calculations yield a valid first order approximation to the observed velocity fields, indicating that the assumption made in inertial current theory is valid. In addition, it has been shown that in geostrophic calculations in this region, the density field may be approximated as a parabolic function of temperature only. A general discussion of mass field adjustment to downstream speed changes is offered.http://www.archive.org/details/onvalidityofgeos00obriLieutenant, United States Nav