His work on the propertiesof vortices led Lord Kelvin to theorize that ether is the only substance in the cosmos, and his interest in the senses led to his invention of the ophthalmoscope and to his influential 1863 book On the Sensation ofTone.  
He lends his name to the eigenvalue equation for the Laplacian, to a type of resonator which works like thebody of a guitar, and to a pair of coils which creates a uniform magnetic field.  His work on the propertiesof vortices led Lord Kelvin to theorize that ether is the only substance in the cosmos, and his interest in the senses led to his invention of the ophthalmoscope and to his influential 1863 book On the Sensation ofTone.  FTP, name this scientist who identified the quantity "internal energy minus temperature timesentropy," which is denoted by a capital F and referred to as his "free energy."
He lends his name to the eigenvalue equation for the Laplacian, to a type of resonator which works like thebody of a guitar, and to a pair of coils which creates a uniform magnetic field.  
Hermann von Helmholtz