Handbuch der physiologischen Optik was published as Vol. Helmholtz's introduction to the work states that it originally appeared in three parts, the first in 1856, the second in 1860 and the third in 1866. Horblit owned a copy in six parts published between 1856 and 1867. --J. Norman, 2006. In Handbuch der physiologischen Optik Herman von Helmholtz (1821-1894) "investigated the optical contents of the eye, measured by his invention, the ophthalmometer, the radii of curvature of the crystalline lens for near and far vision, explained the mechanism of accomodation by which the eye can focus within certain limits, discussed the phenomena of color vision and gave a clear account of the movements of the eyeballs so as to secure single vision with two eyes. In particular he revived and gave new force to the theory of color vision associated with the name of Thomas Young, showing the three primary colors to be red, green and violet, and he applied the theory to the explanation of color blindness" (Enc. Brit. ). "