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physicist who studied the viscosity (resistance to relative motion) of fluids.
This culminated in Stokes' law, F = 6rv, which applies to a force acting
on a sphere falling through a liquid, where is the liquid's viscosity and
r and v are the radius and velocity of the sphere. In 1852 Stokes gave the first explanation of the phenomenon of fluorescence, a term he coined. He noticed that ultraviolet light was being absorbed and then re-emitted as visible light. This led him to use fluorescence as a method to study ultraviolet spectra. Stokes was born in Sligo, Ireland; he studied at Cambridge, where he became professor of mathematics 1849. Stokes's investigation into fluid dynamics in the late 1840s led him to consider the problem of the ether, the hypothetical medium for the propagation of light waves. He showed that the laws of optics held if the Earth pulled the ether with it in its motion through space, and from this he assumed the ether to be an elastic substance that flowed with the Earth. Stokes realized in 1854 that the Sun's spectrum is made up of spectra of the elements it contains. He concluded that the dark Fraunhofer lines are the spectral lines of elements absorbing light in the Sun's outer layers. |