Scientific ContributionsMichell's first major contribution to science was the suggestion that earthquakes originate as an event at a specific location, where the catalyst for this event is the mass movement of rock where offsets in geologic strata are present (e.g. faults). Michell further suggested that because of the earth's elastic properties (Hooke's Law - 1660), it could support the propagation of traveling wave forms. Michell then suggested the source point of the seismic event could be calculated based on measuring travel times of seismic waves at differing points (www.seds.org). Because of his work and observations in seismology, Michell was able to develop theories involving the geology of the earth's crust. Michell understood that the earth was composed of relatively uniform strata, where some of this uniformity had been forced into upheaval or deformation by movement from within the earth.
In 1750, Michell suggested that the magnetic force exerted by each pole of a magnet decreases in proportion to the square of the distance between then. This concept is known as the inverse square law of magnetism. Michell's second contribution to physics dealt with gravity, where he engineered a torsion balance in an attempt to measure the amount of gravity associated with a known mass. This concept is known as the "gravitational constant," and suggests that if one knew the ratio between gravitational and inertial mass, and the strength of gravitational fields of celestial bodies, it would be possible to calculate the mass of those bodies. Michell passed away before completing this work, but the torsion balance was inherited by Henry Cavendish who later continued Michell's work and calculated the Earth's mass. Michell was also known for engineering several of his own telescopic devices. The main instrument used in his celestial studies was one he had built himself- a 10 feet focal length reflector with 30 inch aperture. Upon his death, this instrument was purchased by William Herschel to use as a model for future telescopic designs (www.science clarified.com). In 1767, Michell introduced statistics to field of astronomy. Through his statistical analysis of the Pleiades cluster, he calculated the probability of close grouping of stars in one in five hundred thousand. Michell surmised that double or multiple star systems were likely attracted to one another via gravity, and provided the first evidence of binary stars and star clusters. Michell's last contribution was in 1783, and was the first scientist to proposed the idea of black holes. He reasoned that if Newtown's theory of light was true, it was possible that a star's mass could create a gravitational force that exceed escape velocity's of light. He calculated that this could theoretically occur if a star was 500 times the size of the Sun. He later surmised that if this was the case, such a start would not be visible as light would not be able to escape the gravitational forces (www.realativitybook.com). |
This webpage was created by Corey Miller, for use in GO 521 History of Geology. Dr. James S. Aber, Professor. Emporia State University. Spring 2015. Inset images from top: Wikipedia commons (header/ inset bottom) and Rollins University (middle inset).